Fluid Slip is a term commonly used to describe the migration of liquid around the internal moving parts of gear, lobe, and vane pumps. It is the volumetric difference between physical component displacement and liquid throughput of a pump system. Slip loss refers to the liquid that passes through the clearance space (approximately 0.00005 inches) between the piston and the cylinder wall. Since this clearance represents a restrictive passage of essentially constant dimension, the slip rate is determined by viscosity, pressure and time.
Assuming constant liquid viscosity and pressure, slip will be a smaller factor in a high repetition rate pump (short time per stroke) than in a low repetition rate pump. As viscosity increases and pressure decreases, time becomes a less significant contributor to slip loss. The clearance can be modified to compensate for viscosity. The clearance between the piston and cylinder wall must be optimized for the liquid being pumped in order to minimize the loss due to fluid slip.
In order to minimize fluid slip, the reservoir height and tip height need to be considered. As a general rule, the reservoir height and tip height should be equal. A fluid’s viscosity will play a part in this determination. One way to determine the optimal position of the reservoir and tip is to prime the input and output lines with fluid and observe the output line for fluid movement during idle time. If the fluid moves back in the line, raise the reservoir. If the fluid drips from the tubing, lower the reservoir. The goal is to achieve zero pressure differential over the pump.
Fluid Slip is an important factor to consider through the design and build stages of any pump or pump component. If you have any questions about fluid slip, please send us an e-mail and we would be happy to help.
Usually we try to stay away from any type of valve, since our pumps are valveless and act as their own valve. Recently we ran into a situation where the customer could not purge after the pump was in an idle state for a long period of time (approximately 20-30 minutes). The material was very expensive and hazardous. Moving the reservoir helped a little bit, but regardless the fluid was either going to move forward and drip or move backwards and would then force the user to “waste“ several shots to prepare the pump to dispense again.
It was suggested we use a pinch valve on the inlet, mounted closely to the pump. Extensive testing was done and the results were very good. It is important that the valve opens just before the dispense cycle is triggered and closed as soon as the dispensing cycle has been completed. It is also important to use silicone tubing so it can seal together quickly when pinched but then snap back to its original form when released.
Cases like this are a great example of Ivek’s ability to test and adapt to our customer’s needs. We understand that efficiency is crucial and waste can seriously hurt our clients’ bottom line. We strive to deliver the best precision liquid metering and dispensing equipment for your needs. Contact us today if you have a unique dispensing need.
Often we receive calls from automation and manufacturing companies who have problems with their filling and dispensing needs from other vendors. Typically, a piece of equipment has been installed that doesn’t meet specification or the filling is difficult to control. This problem translates to lost or wasted product, costing the organization a tremendous amount of time and money.
When deciding which OEM pump is best for precise aspirating and dispensing of samples and reagents in both Analytical and IVD instruments, we are often asked the differences between traditional Syringe Pumps and IVEK’s Ceramic Displacement Pumps. Since both of these can be used to do the same function, what are the pros and cons of each?
Which positive displacement pump (PD pump) is best for your dispensing needs, linear or rotary? Linear and rotary positive displacement pumps can provide exceptional accuracy and precision. However, each method has their advantages and disadvantages. Positive displacement pumping refers to a pump that retracts in a cavity to generate volume on the suction side and extends to close in the cavity on the discharge. Fluid flows into the suction side during retract and flows out of the discharge during contraction. This is a constant for each cycle.
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