Neuma Four Channel Leak Test Solution

Neuma Four Channel Leak Test Solution

Neuma LLC. is a production design firm that specialized in Medical Engineering, Packaging, Testing, Electrical Engineering and Sterilization.

The engineers at Neuma like to “transform technologies into medical solutions.” It is with this approach that they integrated four Zaxis PD leak testers into one fixture to create a four-channel concurrent vacuum decay leak tester.

For more information on the Neuma 4-Up Leak Test solution visit their website at: https://neumaengineering.com/project/4-up-leak-test-equipment/

Zaxis PD

Zaxis Pressure Decay Leak TesterAutomatic pressure control allows multiple tests to run at varying pressures without having to adjust the tester. Wall mountable to free up counter space

Neuma Four Channel Leak Test Solution

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Water Hammering, and Cavitation in Pumps

Water Hammering, and Cavitation in Pumps

Newtonian and Non-Newtonian Fluids,Water Hammering, and Pump Cavitation

Newtonian and Non-Newtonian Fluids, Water Hammering, and Cavitation in Pumps

While handling pumping systems, it is critical to have a background understanding of some of the important concepts that govern pump performance, efficiency, output, and longevity. The following resource aims to discuss the concepts of Newtonian/Non-Newtonian fluids, water hammering, cavitation in pumps, and how these factors impact modern pumping systems.

Newtonian and Non-Newtonian fluids

In fluid pumping, it is fairly important to understand the properties of the fluids being pumped, transferred, and mixed. This understanding plays a major role in selecting suitable equipment for fluid pumping. Fluid viscosity or thickness determines the way a particular fluid will behave in a pump. When it comes to fluid viscosity, fluids show a non-uniform pattern. Some fluids maintain a constant viscosity while others show a significant change in viscosity as temperature and applied forces change. 

In general, fluids can be divided into two broad categories. Newtonian fluids and Non-Newtonian fluids. Non-Newtonian fluids have further subcategories (more on that later). Pump manufacturers and end-users must have a clear understanding of these fluid types and their behavior. This plays a vital role while selecting and operating pumps.

Understanding ‘Shear’

Before we move on, it is important to understand the concept of ‘shear’. In very simple terms, shear is the relative motion between adjacent layers of a fluid that is in motion. An example of a fluid in motion is when butter is applied to bread. In this case, there is relative motion between two layers of fluid (butter on the knife and butter on the bread). 

In the case of solids, the shear force acts tangentially to the surface of the solid. A solid can resist deformation due to this force but a fluid will flow under its influence. When adjacent layers of a fluid move relative to each other, shear stresses are developed. Shear forces are developed because adjacent layers of a fluid move with different velocities in a pipe (thus there is relative motion between them). Shear rate is defined as a measure of the extent of this relative motion between the layers.

Shear Stress and Shear Rate

Newtonian Fluids

Newton’s law states that the shear stress is directly proportional to shear rate when fluid viscosity is constant. Fluids obeying this law are called Newtonian fluids. In other words, the fluid viscosity does not change no matter how much shear is experienced by it. In the case of Newtonian fluids, kinematic viscosity is considered. This is the viscosity when no external forces are acting on the fluid. In other words, this is the viscosity when only gravity is acting upon a fluid. The kinematic viscosity of Newtonian fluids remains constant even if external forces are applied to the fluid. Examples of such fluids include water, high viscosity fuel, some motor oils, most mineral oils, gasoline, kerosene, most salt solutions in water, light suspensions of dye stuff, kaolin (clay slurry). These fluids have fairly defined and consistent flow characteristics.

Non-Newtonian Fluids

The viscosity of these fluids changes as shear is applied. This makes them much more challenging to pump. In the case of Non-Newtonian fluids, the Dynamic viscosity is considered and it changes when shear is experienced by the fluid. During pump design, the changing viscosity has to be considered for ensuring appropriate flow, pipe size, and optimum pump characteristics (pump speed; inlet pressure requirements; pump pressure drop to initiate flow). Depending upon how the viscosity changes in response to external forces, Non-Newtonian fluids are further divided into sub-categories. These categories are as follows:

Dilatant

The fluid viscosity increases as shear is applied. They are also called shear thickening. If you quickly try to force an object through such a fluid, it will be met with a lot of resistance. On the contrary, slowly introducing the object will give its molecules the time to move away and the object will move while facing much less resistance. Examples of such liquids include:

  • Feldspar 
  • Quicksand 
  • Beach sand 
  • Clay
  • Mica
  • Silly putty 

Pseudoplastic

In the case of pseudoplastics, viscosity decreases when shear is applied. Examples of such cases are:

  • Grease
  • Soap
  • Sewage 
  • Sludge
  • Molasses
  • Paint
  • Most emulsions
  • Paper pulp
  • Printer’s ink 
  • Starch
Figure 1: Stress response of dilatants and pseudoplastics
Stress over time

Thixotropic

In addition to shear, the viscosity is also time-dependent in the case of thixotropic fluids. The application of shear decreases the viscosity and the viscosity also decreases as time goes by. These fluids include:

  • Silica gel 
  • Greases
  • Bentonite
  • Inks
  • Mayonnaise

Rheopectic

The behavior of these fluids is similar to dilatants (viscosity increases with shear) but the difference is that the viscosity is time-dependent as well as goes on to increase with time. Examples include 

  • Gypsum in water
  • Asphalt 
  • Lard
  • Starch
  • Fruit juice concentrates
  • Molasses
Figure 2: Stress response of Rheopectic and thixotropic fluids
Stress over time

Shear thickening in Non-Newtonian fluids

Under a fast-moving shear force, shear thickening fluids tend to act like solids. The more force is increased, the more their viscosity increases. When pumps are run at high speeds, they produce high pressure as well as fast-moving shear forces. This increases the viscosity of these fluids because the molecules crowd each other under high pressure. On the contrary, molecules have time to move out of each other’s way under low pressure and low velocities which causes a decrease in viscosity. It means that the pump speed and pressure greatly influence the way fluids behave during processing and dispensing. 

A Non-Newtonian fluid tends to resist flow much more than a Newtonian fluid like water. This difference in viscosity has to be taken into account to maximize production efficiency. Viscosity affects how long fluid takes to dispense and its flow rate. Besides viscosity, shear thickening also needs to be considered (it is a fluid’s response to shear forces). For example, ketchup is a shear-sensitive fluid and at rest doesn’t pour well. But in response to squirting (application of forces), it becomes less viscous and pours easily out of the bottle. Honey is not a shear sensitive fluid so squeezing a honey bottle doesn’t affect its viscosity considerably. For pump and piping systems designers, this is important to consider because shear-sensitive fluids like shampoo, ketchup, or egg white need to be handled gently as their composition and integrity can be affected.

Non-Newtonian Fluid

Shear thickening in pumps

As discussed earlier, Non-Newtonian shear-sensitive fluids change in viscosity in response to shear. This means that while passing through the impeller of a pump, the fluid viscosity changes in response to forces exerted by the impeller. Shear thickening fluids (dilatants) increase in viscosity while the viscosity of shear-thinning fluids decreases when forces are applied. Corn starch, for example, is a dilatant, and its viscosity increases when a mixture of cornstarch and water flows out of a pump.

Why are high efficiency pumps important?

Pump efficiency is the ratio of the amount of fluid entering the pump to the amount of fluid leaving it. A pump with higher pump efficiency is more effective for gentle product handling. A low-efficiency pump means that some portion of the product remains in the pump casing and is recirculated. This further impacts the fluid’s viscosity and sometimes the changes in viscosity can be permanent due to overhandling which can result in compromising the product’s integrity. 

To avoid this problem, a positive displacement pump can be used. Such a pump can deliver a constant flow rate at a given pump speed. Even if the viscosity increases, a constant rate of the fluid can be dispensed by ramping up the pump’s horsepower.

Water Hammer and its causes

Water hammer is a surge of pressure that can arise in pumping systems. The pressure is created when the pumping system undergoes an abrupt change in flow. The main causes of water hammering include opening and closing of valves, pump starts and stops, and separation and closure of the water columns. Due to these factors, the water column undergoes a change in momentum and this abrupt change can produce shock waves that travel back and forth within the system. Depending on the magnitude of the shock wave, physical damage in the system can be severe. 

The phenomenon can be understood by an example in which water is pumped in a pipe that has valves on its both ends. The inlet valve is opened and the water column starts traveling towards the discharge valve. At this point, the discharge valve is closed instantly and the leading edge of the water column strikes the closed valve and begins to compress. A pressure wave (shock wave) begins to travel along the backstream (towards the inlet valve). The shock wave travels back and forth between the two valves until it finally diminishes due to friction losses. This water hammer shock wave is so fast that it can make a round trip between the two valves in less than half a second in the case of a 1000 feet pipe. The pressure created by this shock wave depends on the wave velocity (a), the velocity of water in the pipe (V), and the universal gravitational constant (g). Mathematically,

P = a V / 2.31 g

Even at a pipe velocity of just 10 ft/sec, the additional pressure can reach 657 psi. This is a huge amount of pressure that can easily devour pipelines! 

Causes of water hammer

If we examine the causes of this phenomenon, there appear to be three dominant factors:

  • Valve opening and closure
  • Pump start and stops
  • Water column separation and closure

Valve opening and closure

The abrupt closure of valves is one of the primary causes of water hammer. Consider the system in figure 3 below. A branch is feeding the main pipeline and the circuit is in the form of a ‘Tee’. A valve has been installed at the end of the branch. In this case, the primary barrier to water flow is the valve while the secondary barrier is the ‘Tee’.

Figure 3.
Valve opening and closing

If the valve is closed quickly when the water is flowing in the branch line, a shock wave will develop and will travel back and forth between the valve and the Tee. The time of valve closure (i.e. how quickly the valve is closed) also affects the intensity of the water hammer. The following equation gives the relationship between the additional pressure generated by the shock wave (P), flow velocity in ft/sec (V), pipe length between barriers (P), and valve closing time in seconds (t): 

P = 0.07 (VL / t)

The additional pressure is directly related to the flow velocity and length of the pipe between the barriers. It is inversely related to the valve closure time. Since the pipe length is often fixed, the additional pressure caused by the water hammer can be managed by changing the valve closure timing and the flow velocity. 

It is also important to know that water hammering can have more devastating effects in systems designed to operate at low pressures. A 1000 ft pipe with a 5 ft/s flow velocity will experience the same intensity of shockwave whether operating at a pressure of 50 psi or operating at a pressure of 200 psi. The main difference is that the ratio of shock pressure to design pressure will be much higher for a system with a 50 psi design pressure than for a system with a 200 psi design pressure. The damage in the case of the 50 psi system will, therefore, be much greater.

Pump starts and stops

When a pump is started in large pumping systems, it is done so when the discharge valve is closed. The valve is opened slowly only after the pump has reached its maximum speed. Water hammer is significantly reduced when the pumps are started and stopped against a valve that is opened or closed slowly. 

The problem occurs when the pump motor loses power during a power outage. This reduces the water flow at pump discharge and a water hammer is created due to abrupt changes in pressure and kinetic energy of the flowing water. This shockwave can reverse the water direction that can prompt the pump impeller to accelerate in the reverse direction. This creates additional pressure because backflow is reduced when the impeller reaches maximum reverse speed. 

To mitigate this situation, a ‘spring-loaded’ check valve is installed at the pump discharge and a specific value of pressure is maintained at the pump inlet. When the pump starts, it has to create more pressure than that at the pump inlet in order for the flow to initiate. This ensures that the flow is increased gradually and water hammering is not initiated. When the pump stops, the spring-loaded valve is instantly closed. This prevents the water column from changing direction and a relatively uniform pressure is maintained through the pipeline. 

If a normal check valve is used instead of a spring-loaded one, the water column will accelerate backward and slam the check valve close thus initiating a shock wave.

Water column closure and separation

This occurs in a two-phase system when the water column exists as liquid and vapor simultaneously. When the pressure in the pipeline is reduced below the vapor pressure of water, a phase change can occur. This can separate portions of the liquid water column by creating pockets of water vapor in between. When the pressure rises and exceeds vapor pressure, the liquid water column joins again (water column closure) that can create a wave of high pressure. This is how water column closure and separation can cause damage to thin-walled pipes.

Cavitation in pumps

When the liquid turns to vapor at low pressure, cavitation occurs in pumps. It happens due to a lack of sufficient pressure at the suction end of the pump or insufficient Net Positive Suction Head (NPSH is the difference between the pressure available at the pump inlet and the vapor pressure of the liquid). Cavitation occurs when the pressure and temperature of the liquid at the suction side of the impeller equals the vapor pressure. This creates air bubbles at low pressure. When the liquid travels from the suction side of the impeller to the delivery side, these air bubbles collapse. The force generated when the bubbles implode is often strong enough to damage pump components, seals, shafts, bearings, and impellers. Cavitation can also cause vibration that causes mechanical damage and thus the service life of pumps is reduced.

cavitation

Why does cavitation occur?

Under normal conditions, liquids have a predictable and steady vapor pressure. When the pressure inside the pump falls below the vapor pressure, cavitation occurs. This drop in pressure is often caused by disruptions in flow. Disruptions in flow can be caused by:

  • Poorly specified pump
  • Higher than expected viscosity
  • Clogged inlet
  • Clogged filters and strainers

In addition, at very high discharge pressures, a portion of fluid cannot discharge from the pump. The undischarged fluid gets trapped between the impeller blades and can cause a pressure drop at high velocity. This pressure drop triggers cavitation.

Recognizing pump cavitation

Typical signs of cavitation include:

  • Vibration
  • Impeller erosion
  • Noise
  • High power consumption
  • Seal or bearing failure

Cavitation usually sounds like gravel or marble moving inside the pipe, pump, or hoses. 

NPSHa and NPSHr

A clear understanding of the NPSHa and NPSHr is critical for understanding the cavitation process. The NPSHa (Net Positive Suction Head Available) is a system-specific value and doesn’t depend on the pump. It is the difference between the pressure at the pump inlet flange and the vapor pressure of the liquid. In short, the head available at the pump suction flange pipework connection is the NPSHa. 

NPSHa = Pressure at pump inlet – vapor pressure

The NPSHr (Net Positive suction Head Required) is not related to the system and is a purely pump specific property. It is the minimum pressure at the pump suction port that will prevent the pump from cavitating. The NPSHr alone is not sufficient to keep the pump from cavitating because it is measured just as cavitation begins to start. Therefore, the NPSHa should always be greater than NPSHr to keep a positive margin and prevent cavitation.

Steps to avoid pump cavitation 

The main focus should be to prevent unnecessary pressure drop. Additional pressure drop can often be avoided by removing as many valves and bends as possible and moving the pump closer to the fluid source. The distance between the fluid source and the pump should be decreased if the suction lift requirement is too high and would cause a pressure drop. 

Sometimes there are blockages in the piping or hoses near the pump so enlarging suction lines can mitigate the problem. The suction lines should also be cleaned regularly. In addition to these basic steps, there are a few other effective ways to curb cavitation. 

Pump selection

Cavitation is increased when the pump head drops so selecting the correct pump ensures a positive margin of the NPSHa above NPSHr. Keeping the pressure at the pump inlet 10% greater than the pump specific NPSHr is a good general rule to prevent cavitation. For an NPSHr of 10 feet, an 11 feet NPSHa is a good value. Contrary to NPSHr (which is a pump specific value and cannot be changed), the NPSHa is a system-specific value and can be increased by the following steps:

  • Elevating the supply tank
  • Raising and maintaining tank liquid level
  • Cleaning debris inside the pipes
  • Reducing piping losses caused by unnecessary valves and fittings

Preventing discharge cavitation

Discharge cavitation is observed when the pressure at the discharge end of the pump is very high. This limits the volume of the fluid exiting from the pump and high-velocity fluid remains trapped between the impeller and housing. This is a major cause of cavitation. Causes of high discharge pressure include pipe blockages, poor piping design, and clogged filters. 

To prevent discharge cavitation, reducers should be kept as close as possible to the pump. In addition, pockets should be avoided that allow air and vapor to accumulate. The control valves (if they are needed) should always be installed on the discharge side instead of the suction side of the pump.

Ensuring pump maintenance

Ensuring routine pump maintenance is a proven method to avoid cavitation. The maintenance activities can include:

  • Cleaning blocked filters and strainers to avoid discharge pressure buildup. A maintenance schedule should be set up for regular cleaning. 
  • Checking the pressure sensing equipment. 
  • Ensuring that there are no cracks or collapsed points in the piping and hoses.

 

Installing the system properly

The system should be designed such that the NPSHa is greater than the NPSHr. There are four factors that have to be considered for an appropriate system design:

 

Pump location

The pump should be installed in such an orientation that the pump suction inlet lines have an adequate slope and the pump housing is flooded. It should be ensured that the fluid flows smoothly into the pump suction inlet. 

The pump should be placed at a level that is lower than the fluid level in the supply tank. This pump orientation involves the force of gravity to maintain the flooded section of the pump. This helps to curb cavitation.

Size of the suction pipe

The pump suction diameter should be chosen carefully. This helps to maintain laminar flow. It is best to avoid elbows, valves, reducers, and strainers in the final length of the pipe. 

In addition, the pump casing should not be made to support the weight of the piping. This can cause strain on the pump casing. The piping should be supported on supports and hangers. The suction side of the pump should be always kept larger in size than the pump inlet.

Suction lift

The suction lift is the vertical distance from the water source to the pump inlet. A high suction lift can increase turbulence, ramp up energy demands, and most importantly, decrease NPSHa. The pump should therefore always be installed below the water level in the supply tank.

Friction loss

Friction loss in the piping system results in pressure drop that can cause cavitation. Friction losses are affected by pipe length, diameter, and flow rate. Obstructions in flow velocity can cause pressure changes that can trigger cavitation. 

In conclusion, there are a number of factors that initiate cavitation. If any trouble is encountered, the following list of quick checks can help in troubleshooting:

  • Checking whether the pump is installed high above the fluid source or not
  • Checking whether the pump suction line is sloped properly or not
  • Checking if there are unnecessary fittings on the suction pipe
  • Checking if the pump is running too fast
  • Checking if the suction pipe diameter is too small or the pipe is too long

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Metering Pump Technologies

Metering Pump Technologies

Metering Pump Technologies

Delivery of a fluid in precise and adjustable flow rates is called metering. A metering pump is a device used to control the flow rate of a fluid. It is used to move a precise volume of liquid in a specified amount of time to provide an accurate volumetric flow rate. Typically, water, chemicals, solutions, and other fluids are moved by a metering pump. The flow rate depends on the outlet pressure and is usually constant over time. A metering pump is designed to deliver a maximum discharge pressure so the selection of a suitable pump depends on the type of application. A vast majority of metering pumps can be categorized as positive displacement pumps. 

Positive displacement pumps

Positive displacement pumps move the fluid by repeatedly enclosing its fixed volume and then moving it mechanically through the system. The fluid moving mechanism (pump action) can be executed through gears, pistons, plungers, rollers, screws, vanes, and diaphragms. The majority of positive displacement pumps can be categorized either as reciprocating type or rotary type.

Reciprocating positive displacement pumps

These types of pumps use a piston, plunger, or a diaphragm to execute a stroke (repeated back and forth movements). These movements are known as reciprocating motion. 

These cyclic movements of reciprocating pumps create a pulsating flow at discharge where the flow accelerates during the compression stroke and decelerates during the suction stroke. This requires different kinds of damping mechanisms to be installed to minimize the vibrations that result from pulsating flows. If left unchecked, these vibrations can have damaging effects on the installations and equipment. Vibrations and pulsating flow can be reduced if multiple pistons, plungers, or diaphragms are used where one group is in compression stroke while the other is in suction stroke.

Reciprocating pumps are ideal for places where accurate metering is required because of their repeatable and predictable motion. Specific quantities of fluids can be pumped by adjusting the stroke length and stroke rate in these pumps. 

Piston and plunger pumps

In piston pumps, the initial stroke starts the suction phase. During this stroke, vacuum is created, the inlet valve opens, the fluid is drawn in, and the outlet valve is closed. The next stroke of the piston is in the reverse direction and starts the compression phase. The inlet valve closes while the outlet valve opens, allowing the fluid to move out of the chamber. The inlet and outlet valves operate 180 ᵒ out of phase that causes one valve to open while the other is closed. A seal is installed on the piston that prevents leakages. 

The operation of a plunger pump is similar but in this case, the volume of the fluid moved depends on the plunger size. In the case of a piston pump, this volume depends on the cylinder volume. The seal is installed on the cylinder housing instead of the plunger.

Benefits: 

  • Piston and plunger pumps are very suitable for low specific speeds and high-pressure heads.  
  • These pumps are self-priming which means that they can evacuate air from the suction side at startup before commencing the normal pumping mode. 
  • They can handle a wide range of pressure and can move thick fluids and abrasives with relative ease. 
  • These pumps are ideal for delivering a known quantity of fluid precisely. They have low energy consumption while having significantly high efficiency.
  • A wide variety of fluids can be pumped including hot, cold, toxic, corrosive, abrasive, viscous, and flammable fluids.  

 

Limitations: 

  • The piston and plunger pumps can only deliver a pulsating output instead of a smooth continuous flow. No fluid is discharged during the suction stroke which results in a pulsating flow. This type of flow is the cause of vibrations that can cause damage to the equipment. To cater to this issue, additional damping or smoothing equipment needs to be installed. 
  • In the case of large units, often the investment costs for a single pump can be on the higher end. 
  • The moving parts of this pump are in contact with the fluid so there is a greater frequency of mechanical wear. This results in higher maintenance costs. 

Diaphragm pumps

In the case of a diaphragm pump, the piston or plunger is replaced by a flexible membrane. This flexible membrane or diaphragm is connected to a rod that is used to expand and compress the diaphragm. The volume of the pumping chamber is increased by expanding the diaphragm. This creates suction and draws the fluid into the chamber. When the diaphragm is compressed, the volume of the chamber is decreased and some fluid is expelled out. 

Benefits: 

  • Because of completely airtight seals, diaphragm pumps are often used to pump hazardous fluids.
  • These pumps can handle fluids with high viscosity. Because there are no rotating and close-fitting parts, fluids with high solid and abrasive content can be easily pumped. This also helps these pumps to run dry without the risk of significant damage. 
  • Their efficiency remains constant over time because there is no wear and tear associated with moving parts. 
  • Diaphragms pumps are used for a wide spectrum of applications because of their adjustable flow rate and discharge pressure which can be controlled by adjusting stroke length and rpm. 
  • The maintenance requirements for these pumps are significantly low because of the absence of mechanical seals, couplings, and motors. 
  • These pumps are portable and can be quickly transported where required.
  • Diaphragm pumps come to a halt when the discharge pressure exceeds air pressure. The discharge line is close with no power consumption and no increase in temperatures. 
  • A significantly high discharge pressure can be achieved through these pumps. Mechanical diaphragms pumps can provide a pressure of around 60 to  250 psig while hydraulic diaphragm pumps can pressurize fluids up to 4000 psig.

Limitations:

  • The flow is pulsating. It accelerates and decelerates during compression and suction strokes respectively. A damping mechanism must be installed to reduce pulsation.
  • The check valves located at intake and discharge sections can become clogged if the fluid contains a higher percentage of solid particles. This can result in a loss in the suction and priming ability of the pump which can lead to inaccurate metering. Because of this limitation, these pumps require frequent maintenance.

Rotary positive displacement pumps

In these pumps, rotating gears and cogs are used to transfer fluid instead of the backward and forward motion associated with reciprocating pumps. A suction is created at the pump inlet when the rotating gear or cogs develop a liquid seal with the pump casing. After the fluid is drawn inside the pump, it gets enclosed between the rotating teeth of the gear or cogs and is then transferred to the discharge section. During this process, energy is transferred to the fluid, and its pressure increases. The gear pump is one of the most common examples of a rotary positive displacement pump.

Gear pumps

Gear pumps use the rotation of gear teeth to transfer fluids from the inlet section to the discharge section. The gears apply force on the entrapped volume of the fluid and its pressure is increased during the process. A pair of spur or helical gears is normally used in the process. These gears revolve in opposite direction. The fluid is trapped between the teeth of the moving gears and is carried from the suction side to the discharge side. Due to this movement of the gears and low tolerance between the casing and gear teeth, a negative pressure zone is created on the suction side. This draws fluid inside where it is trapped between the gear teeth. The fluid is then carried towards the discharge and its pressure is increased in the process.

Benefits:

  • Gear pumps can operate at high pressures and can be used with high viscosity fluids. 
  • Despite being low cost and having a relatively simple structure, they can deliver results with up to 0.5% accuracy.
  • Their output flow is free from surging pulses that are observed in piston and plunger pumps. The pulses in flow are also less as compared to diaphragm pumps. 
  • The system design is simplified because no vibration-damping equipment is required.
  • Fluid leakage can be eliminated using hermetically sealed magnetic couplings.
  • The operation, handling, and maintenance of these pumps are relatively straight forward. 

Limitations:

  • The low tolerance between the gear teeth and the casing can be affected by abrasive fluids. This can result in leakages and changes in suction pressure. 
  • Abrasive fluids can cause wear on the gear teeth and around the face of the gears. This can lead to frequent maintenance requirements. 
  • Due to wear, the efficiency of these pumps can decrease over time.
  • The phenomenon of flow slip can occur which leads to backflow of the fluid from the discharge side to the suction side.
  • Pump output can be affected as flow slip increases. This can also affect metering accuracy. 
  • Despite being capable of self-priming (because rotating gears can evacuate air of the suction line), this ability can be restricted to 1 ft. lift. 

Peristaltic pumps

In peristaltic pumps, the pump casing contains a hose or a tube in which the fluid is contained. The tube is alternatively relaxed and compressed by means of a roller. This creates a vacuum that draws the fluid through the tube.

Benefits:

  • The fluid is always enclosed within the casing and is never in contact with the pump mechanism. This eliminates the chances of the pump contaminating the fluid and vice versa. 
  • The complete closure of the tube when it is squeezed between the roller and track prevents backflow when the pump is not running. This eliminates the need to install separate check valves when the pump is not running. 
  • Because of a lack of seals and valves, these pumps are easy and less costly to maintain. 
  • The pump is capable of self-priming and has the ability to run dry. 
  • Cleaning the tube and hosing is a simple process.
  • Peristaltic pumps can easily handle viscous fluids and slurries.

Limitations:

  • The cyclic action of these pumps creates pulses in the discharge that has to be catered by introducing additional pumping elements and hoses.
  • These pumps are generally limited to 40 to 60 psig discharge pressure. 
  • The flexible tubes and hosing need to be replaced periodically as they are prone to degradation over time.
  • The drive motor is constantly under load because the rotor has to continuously squeeze parts of the tubing. This can increase power costs associated with the motor. 
  • The suction lift is limited by the strength of the tubing wall.

The eVmP Reciprocating and Rotating Pump

The eVmP (electronic variable metering pump) manufactured by Z-axis is an electronically controlled, rotating, and reciprocating pump that combines the benefits of rotating and reciprocating technology. This pump design is a major improvement because it eliminates the need for discharge valves which results in only one moving part (the ceramic piston). This drastically reduces the wear and tear associated with the relative movement of mechanical components and ensures up to 84,000,000 maintenance-free cycles.

The pump technology ensures remarkable accuracy because of extremely tight tolerances between the piston and the liner. This ensures extremely precise metering and volume control of the fluid being dispensed. This valve-less design ensures that the inaccuracies associated with tubing and diaphragm pumps are eliminated. Through its electronically controlled linear stepper actuator, ultrafine adjustments to piston travel distance and angle position are possible. This means that the volume being dispensed can be controlled with the push of a button. This also enables the pump to overcome variations in fluid viscosity and surface tension through dynamic fluid displacement. Overall, the Z-axis eVmP is one of the finest, valveless, positive displacement pumps that is fully automated and provides a safe and accurate way for precise metering and dosing of fluid without the design complexities and additional costs associated with other pumps in the market. 

    The pump technology ensures remarkable accuracy because of extremely tight tolerances between the piston and the liner. This ensures extremely precise metering and volume control of the fluid being dispensed. This valve-less design ensures that the inaccuracies associated with tubing and diaphragm pumps are eliminated. Through its electronically controlled linear stepper actuator, ultrafine adjustments to piston travel distance and angle position are possible. This means that the volume being dispensed can be controlled with the push of a button. This also enables the pump to overcome variations in fluid viscosity and surface tension through dynamic fluid displacement. Overall, the Z-axis eVmP is one of the finest, valveless, positive displacement pumps that is fully automated and provides a safe and accurate way for precise metering and dosing of fluid without the design complexities and additional costs associated with other pumps in the market. 

    Benefits: 

     

    • Mechanical wear is eliminated because there is just a single moving part. There is no relative motion between parts which is a major cause of wear and tear.
    • Extremely precise and accurate metering and dosing is possible owing to tight tolerances between the piston and the liner wall.
    • Metering volume can be controlled electronically through the push of a button. 
    • Since there are no valves, there is no clogging which removes the need for constant maintenance and servicing. 
    • A drift free operation is ensured because of the ceramic body. 
    • A wide range of fluids including acids, bases, and solvents can be used because of the inertness of the ceramic material.
    • Because of a positive displacement design, the pump’s accuracy and precision remain unaffected even as the viscosity of the fluid changes. 
    Covid 19 Response Thank You from Air Logic

    Covid 19 Response Thank You from Air Logic

    Covid 19 Response Thank You from Air Logic

    2020 was a hard year and many of us had to adapt and react quicklyin response to the fight against Covid-19. Air Logic sent our employees this wonderful thank you video. We are proud to have partners like Air Logic and we look forward to many more years and projects together.

    iKit Leak Tester

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    The Ideal Gas Law & Leak Testing Video

    During leak testing, changes in pressure can occur due to changes in temperature, volume, and number of moles of the gas.

    The Ideal Gas Law & Leak Testing Video

    The Ideal Gas Law & Leak Testing Video

    In this video we will discuss the ideal gas law and its effects on leak testing.

    During leak testing, changes in pressure can occur due to changes in temperature, volume, and number of moles of the gas. Since parameters like pressure, volume, and amount of air are involved in this process, it is governed by the ideal gas law.

    PV = nRT

    Where:

    P = the Pressure of the air (or gas) enclosed in the container, measured in atmospheres

    V = the Volume of the container occupied by the gas, measured in Liters

    n = the Number of moles of the gas

    R is the Ideal gas constant with a value of 8.314

    & T = the Absolute temperature of the gas, measured in Kelvin

    Changes in pressure, temperature, and volume are related and a change in any single parameter can affect other parameters.

    When the temperature of air rises, the average kinetic energy and velocity of the particles increases.  This raises both the pressure and temperature.

    When the test part is pressurized, the walls of the part can undergo expansion. This causes a change in the volume of the part. With an increase in area, the overall pressure drops. Similarly, a decrease in volume causes an increase in pressure, so long as the temperature and number of moles are constant. If the number of particles increases, this exerted force per unit area also increases.

    Using the ideal gas law, a suitable relation can be derived that allows determination of leak rates through pressure loss in the part. A leak rate can be seen as the volume of gas that escapes through the part per second.

    During a leak test, if the separation of the results, or Delta P, between leaking and non-leaking parts is not great enough, the repeatability of the process will be compromised. This is due to environmental factors influencing the pressure and temperature of the part under test.

    The selection of Fill and Settle times during the test influence the part’s ability to come to equilibrium, which directly affects the test outcome. The greatest contributor to successful test outcomes is the Fill step. At higher test pressures, a longer fill step will allow the thermodynamic process to reach equilibrium. Parts that have more compliance, or capability to experience expansion, also need to reach a point of equilibrium. The ideal gas law illustrates how reducing or nullifying pressure or thermodynamic change will influence test repeatability by causing greater separation in the ΔP, thus improving the test.

    If you have questions about leak testing your part or application visit zaxisinc.com, email sales@zaxisinc.com or call us directly at 801-264-1000.

    Click Here to read full PV=nRT & Leak Testing white paper.

    Request a Quote

    Our leak test experts can help you create the perfect leak tester for you specific application. Call Zaxis today at 801-264-1000 or fill out our RFQ form.

    Neuma Four Channel Leak Test Solution

    Neuma LLC. is a production design firm that specialized in Medical Engineering, Packaging,...

    Covid 19 Response Thank You from Air Logic

    In response to Covid 19 many companies had to react and adapt quickly. Air Logic sent our employees this wonderful thank you video.

    The Ideal Gas Law & Leak Testing Video

    During leak testing, changes in pressure can occur due to changes in temperature, volume, and number of moles of the gas.

    Ideal Gas Law & Its Effects on Leak Testing

    Pressure, volume, moles, and temperature During leak testing, changes in pressure in the test part...
    Ideal Gas Law & Its Effects on Leak Testing

    Ideal Gas Law & Its Effects on Leak Testing

    Pressure, volume, moles, and temperature

    During leak testing, changes in pressure in the test part are of primary interest. When a test part is filled with air (or any other gas), it initially expands inside the part to occupy its volume. When the part finally reaches the test pressure, the air inside contracts. This rapid expansion and contraction of air changes its temperature and volume. The test part also undergoes slight changes in temperature and volume because of changes in temperature and volume of the air. 

    In order to detect the leakage, the changes in pressure must be taken into consideration. The changes in pressure can occur due to changes in temperature, volume, and number of moles of the gas. Since parameters like pressure, volume, and amount of air are involved in this process, it is governed by the ideal gas law. Mathematically, the law is expressed as:

    Ideal Gas Law & Leak Testing Information Video

    P = Pressure of the air (or gas) enclosed in the container

     

    V = Volume of the container occupied by the gas

     

    n = Number of moles of the gas

     

    T = Absolute temperature of the gas

     

    R = Ideal gas constant with a value of 0.0821 dm3 atm K-1 mol-1

     

    According to equation (1), the product of the pressure and volume of any quantity of an ideal gas is equal to the product of the number of moles, ideal gas constant, and the absolute temperature of the gas. It can be seen from equation (1) that changes in pressure, temperature, and volume are related and a change in any single parameter can affect other parameters. 

     

    According to the Kinetic Molecular Theory (KMT) of gases, temperature is proportional to the average kinetic energy of a given sample of gas. This can be expressed as: 

    Equation (1) relates the actual experimental behavior of gases while equation (2) relates the results of experimental analysis using KMT. Studying equations (1) and (2), we can see how pressure, temperature, and volume are inter-related during leak testing. This means that changes in temperature, test part volume, and number of moles of a gas can affect the part’s pressure during leak testing. 

    Effect of temperature changes on the test part’s pressure

    When the temperature of air increases, the average kinetic energy and velocity of the particles increases. This is expressed in the equation (2) above. These particles now have a greater velocity, and they hit the walls of the part with greater force. The pressure exerted by these particles is in essence the force exerted per unit area of the walls of the part. So the pressure increases with an increase in temperature. Pressure is directly related to the temperature when the volume of the container and number of moles of gas are constant. 

     

    Effect of volume changes on the test part’s pressure

    When the test part is pressurized, the walls of the part undergo expansion. This causes a change in volume of the part. When the part expands and its volume increases, the pressure inside drops. This happens because the increase in volume increases the area of the walls. So the force per unit areas (pressure) drops because the force is constant. At constant temperature, the particles have the same average kinetic energy (or velocity) and they exert the same force on the walls. With an increase in area, the overall pressure (force per unit area) drops. Similarly, a decrease in volume causes an increase in pressure if the temperature and number of moles are constant. 

      

    Effect of number of moles on the test part’s pressure

    An increase in the number of moles of the gas increases the pressure inside the part when the temperature and volume are kept constant. Pressure is generated inside the part when the particles exert force on the walls of the part. With an increase in the number of particles (number of moles) increases, this exerted force per unit area (pressure) also increases. 

     

    Accounting for the leak rates caused by pressure changes

    In order for detecting the leak rates correctly, the fluctuations in pressure caused by the factors explained above should be allowed to settle. Oftentimes, this is not the case and in practice, leak testing is carried out without a proper fill and settle time. In order to account for these pressure changes, an adequate relation is needed that accounts for the pressure losses. 

     

    Deriving the relation of pressure loss to leak rate 

    Using the ideal gas law, a suitable relation can be derived that allows determination of leak rates through pressure loss in the part. A leak rate can be seen as the volume of gas that escapes through the part per second. This relation can then later be modified to account for the effects of changes in pressure, temperature, volume, and number of moles.

     

    From the ideal gas law, the number of moles in the test part can be expressed by: 

    If,

    NL = Number of moles of gas lost

    P = PATM = Atmospheric pressure

    V = L.R = Leak rate or volume of gas escaping per second

    Then equation (3) becomes: 

    Therefore, the remaining number of moles NR will be:

    Using ideal gas law, at a constant temperature, the remaining pressure after time (t) can be given by:

    Putting the value of NR from equation (5) in equation (6) and solving for PR, we get:

    Solving for leak rate (L.R) yields:

    Modified equation for accommodating the pressure losses. Equation (7) gives the relation for calculating leak rates when the test volume, temperature and PATM are considered constants. As described above, the actual leak rates (or pressure changes) are affected by changes in volume, and/or temperature. 
    To accommodate these pressure changes, a master part or ‘non-leak part’ is put under test. Despite no real leakage, some pressure change occurs in this non-leak part because of the reasons described above. This pressure loss is called the ‘zero offset’ factor. Equation (7) can then be modified after considering the ‘zero offset’ factor. The modified equation can be used to determine leak rates in test parts. The zero offset factor or the pressure loss of the non-leak part is subtracted from the pressure change of the test part in consideration. By doing this, the pressure changes due to temperature and volume are accommodated for and correct leak rates can be determined. The modified equation is:

    Where,

    L.R (t)       Leak rate (scc/s)

    t                 Time (sec)

    ΔP test          Pressure loss in the test part during the test (psi)

    ΔP non-leak    Pressure loss in the non-leak part (psi)

                  Volume (cubic cm)

     

    Process repeatability

    If the difference between ΔP test and ΔP non-leak is not great enough, the repeatability of the process will be compromised by environmental factors influencing the part under test. The selection of Fill and Settle times during the test will directly affect the test outcome. The greatest contributor to successful outcomes will be from the Fill step. Parts that have more compliance (capability to experience expansion) will need to reach a point of equilibrium. At higher test pressures, a longer fill step will allow the thermodynamic process also to reach equilibrium. Reducing or nullifying these two factors will cause a greater difference in the ΔP, thus improving the test.

    Press Release – zHMI

    Press Release – zHMI

    Press Release: Zaxis has released the zHMI factory automation software that facilitates remote monitoring and configuration of Zaxis devices.

    Download Press Package

    SALT LAKE CITY, UT. (November 19, 2020) –The zHMI factory automation software has been developed by Zaxis to facilitate remote configuration and monitoring of Zaxis devices. zHMI software is currently available for purchase from any Zaxis sales representative.

    The new Zaxis Human Machine Interface (zHMI) software can monitor up to 30 devices at once. The user-friendly interface makes operations such as start/stop or changing device parameters simple for individual devices or updating every device connected at once. The software can display live production statistics and save production history. The zHMI has a simple backup and restore function that will save important device settings.

    Full remote control of Zaxis devices means no more in-person monitoring on the production floor. No more gowning-up in a clean room just to check progress or update a parameter. Many production lines today have large screens around the factory for simple production monitoring, the zHMI is perfect for this application.

    The zHMI factory automation software is currently compatible with PC computers. Simply plug Zaxis devices into a wireless router and get full remote monitoring and control.

    Download Press Package

    Determine a Leak Rate – Live Discussion

    Determine a Leak Rate – Live Discussion

    Determine a Leak Rate – Live Discussion

    What is a Leak Standard?

    A leak standard is a calibrated, simulated leak that can be used in circuit with the part under test. A leak standard can be used during test setup to help you determine the parameters for your leak test. It can also be used to challenge your system by comparing multiple leak systems to each other.

    Neuma Four Channel Leak Test Solution

    Neuma LLC. is a production design firm that specialized in Medical Engineering, Packaging, Testing, Electrical Engineering and Sterilization. The engineers at Neuma like to "transform technologies into medical solutions." It is with this approach that they integrated...

    Covid 19 Response Thank You from Air Logic

    In response to Covid 19 many companies had to react and adapt quickly. Air Logic sent our employees this wonderful thank you video.

    The Ideal Gas Law & Leak Testing Video

    During leak testing, changes in pressure can occur due to changes in temperature, volume, and number of moles of the gas.

    Ideal Gas Law & Its Effects on Leak Testing

    Pressure, volume, moles, and temperature During leak testing, changes in pressure in the test part are of primary interest. When a test part is filled with air (or any other gas), it initially expands inside the part to occupy its volume. When the part finally reaches...

    Configure a Leak Tester

    Contact us today to find the right solution for your needs.

    Leak Testing for Cellular Manufacturing

    Leak Testing for Cellular Manufacturing

    Cellular manufacturing is a lean manufacturing model. The goal of cell manufacturing is to save time and space on the assembly floor by grouping machines together by the specific task they accomplish. These grouped machines, or “cells” are then lined up in the form of an assembly line. The Zaxis PD has been specifically designed to fit in a manufacturing cell.

    Lean manufacturing is a methodology developed by Toyota and defined by James Womack and Daniel T. Jones in 1996 in their book Lean Thinking: Banish Waste and Create Wealth in Your Corporation. Womack and Jones define lean manufacturing as any system that follows the following standards; “Precisely specify value by specific product, identify the value stream for each product, make value flow without interruptions, let customer pull value from the producer, and pursue perfection.” (Lean Thinking p10)

    Using the lean methodology, the concept of cell manufacturing was created to streamline assembly line flow. As seen in figure 8-4 from The Toyota Way, a common cellular manufacturing format is a U-shape which promotes good communication between workers. In a fully automated assembly line, the U-shape can make monitoring the entire line easy.

    When integrating a leak tester into a cell-based manufacturing format, the most common issues are size and information displays. Large testers take up valuable space and often need to be moved away from the line and connected to products via long hoses. This adds excessive volume to the leak test effecting test accuracy. Some smaller testers can be placed right on the assembly line as close to the products as possible but many of these testers have had their displays removed to save space.

    This figure from The Toyota Way shows the design of a U-shaped cell, graphing the paths of two employees through it. (https://commons.wikimedia.org/wiki/File:Figure_8-4_from_The_Toyota_Way.png)

    The Zaxis PD was designed to be perfectly integrated into manufacturing cells. With the size of a 6” cube, the Zaxis PD is compact enough to fit right on the assembly line close to the product. This consolidates the UTT (Unite Under Test) keeping test accuracy high. In spite of the small size a clear LCD color touchscreen is integrated directly into the Zaxis PD. The integrated touchscreen enables at-a-glance leak test monitoring on the production floor.

    Every detail of the Zaxis PD was fashioned for ease of use in a cell manufacturing environment.

    • Wall mounting plates for easy instillation
    • Integrated leak standard port and with dedicated valve
    • Onboard processing
    • USB port for simple data collection
    • Automatic pressure control that allows multiple tests to run at varying pressures
    • Bottom mounted connectors to minimize internal test volume and simplify connectivity

     

    Visit our downloads page for more information and to download the Zaxis PD data sheet.

    Click here to request a quote or call us at +1-801-264-1000.