What is Fluid Slip?


What is Fluid Slip?

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 contact us and we would be happy to help.

Plastic Machining or Injection Molding Debate

Plastic Machining or Injection Molding Debate

Why pay for expensive tooling when you can have a part like this at a fraction of the cost? We’ve been getting a lot of questions on the subject of Plastic Machining vs. Molding.

If you are at the cross road of determining whether your required plastic component should be produced by machining or injection molding, here are some facts to consider. The most obvious question is “what is the plastic”? There are many plastics that cannot be molded, or can cause issues depending on expectations for the finished part, especially if a smooth uniform surface is required. The process of transferring plastic into a mold leaves behind surface imperfections on the finished product. During the injection molding process, plastic flows through runners and is introduced into a cavity through a gate. The gate meters the flow of plastic as it fills the part. The consequence of the gate is that when the finished parts are removed from the mold, the gates leave a slight cosmetic imperfection. In addition, many molds use knockout pins to push the part out of the cavity after cooling. These pins leave a slight depression in the place where they contact the part.

Here is What Machining Plastic Can Provide

Machining plastic materials offer minimal tooling and no expensive molds are required.

When the need for part re-designs and revisions are necessary, the transition becomes easy, seamless, fast and cost effective. Machining plastic parts can provide certain materials with closer and tighter tolerances.

When machining plastic components you get unlimited material options, many of which would be impossible to mold. Threads and undercuts with multiple angles can be incorporated into the part with ease.

*Always keep this in mind once you create a mold, you cannot easily change it. Revisions, updates even slight changes will be costly.

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