Autotutorial for Peristaltic Pumps

How do they work?

Peristaltic pumps are positive displacement pumps utilizing flexible tubes full of liquid and a rotor. Positive displacement means that a set amount of flow rate will be delivered to the system regardless of the pressure on either side. As the rotor turns, it squeezes the flexible tubing, forcing a specific amount of fluid out of the pump.

Pump Speed

The rotor on the peristaltic pump sets the pump speed by how many revolutions per minute that the rotor will turn. We have two types of pumps we currently utilize, one can vary between 1-100 rpm and the other can operate at up to 600 rpm.

Flexible Tubing Sizes

For each tubing size, different pump speeds will correspond to different flow rates being output by the pump.

The peristaltic tubing sizes are rather arbitrary and are labeled by numbers: 13, 14, 16, 17, and 18 in increasing order of size. There is also 3-stop tubing available, which are color-coded based on their ID and must be used with 6-roller pump heads.
The table below gives you an idea of the flow rates that can be achieved by a peristaltic pump for different tubing sizes.

A Mathcad sheet with equations to help select tubing sizes for 6 roller pums and chemical stock concentrations or for 3 roller pumps is available for your use! 
From these charts, you can easily calculate a pump speed given a tubing number and flow rate. At the appropriate tubing number, divide the given flow rate by the flow rate at 1 rpm.

What tubing size and pump speed would you use to acquire a flow rate of 500 mL/min? Keep in mind that you can use more than one pump head...

Working with Microbore Tubing

When working with pump tubing of small size (#13, #14, Orange-Yellow, and Yellow-Blue), it is necessary to use microbore tubing to hydraulically connect the pump to the experimental apparatus. The microbore tubing most commonly used in the lab is PTFE with OD of 1.6 mm (1/16") and ID of 0.8 mm (1/32"). This tubing can be purchased at Cole-Parmer. To connect the microbore tubing to the peristaltic pump tubing requires a barbed tube fitting sized for tubing of 1/16" ID  (can be purchased at McMaster-Carr), shown below.

(Note: In the following steps, a small semi-clear fitting is shown to illustrate the process. This type of fitting can split after undergoing the procedure shown below, so larger 1/16" fittings, like the one shown above, are recommended.)

This barbed tube fitting inserts easily into the small diameter pump tubing as shown below.

Connecting the microbore tubing to barbed fittings poses more of a challenge, since the barbed fitting is designed to fit inside a tube of 1/16" ID, but must instead fit over a tube of 1/16" OD. This would not be possible if not for the ductility of the microbore tubing. In stretching the microbore tubing, its diameter is decreased, and can be stretched to fit within the barbed fitting. Stretching can be accomplished in a number of ways, but the recommended approach is to use the puller shown below.

After coiling the microbore tubing tightly around its spool, the puller can be used to grip the microbore tubing and stretch it, as shown below.

Stretching can also be accomplished by wrapping the tubing around the handle of a screwdriver, for example, in the absence of the puller.

Once the tubing is sufficiently stretched, locate the section of tubing where the cross section is narrowest. It is here that the tubing should be cut so that it can be pulled through the narrow opening. When cutting, try to make the cut at an acute angle, as shown below, so that the tubing will fit even more easily into the opening of the barbed fitting.

If the tube has been stretched enough and the cut has been made neatly, it should be fairly easy to pull the tubing through the narrow opening of the barbed fitting. Once the tubing comes out the other side of the fitting, pull it through until it fits snugly in the opening of the fitting, as shown below.

Once the tubing is secure in the fitting, any excess can be removed and the other side of the barbed fitting can be inserted in the pump tubing as shown below.

The same process of stretching the microbore tubing to fit it snugly into the barbed fitting can be used for other applications. One common application is to bore a hole 1/4" push-to-connect plug so that the plug can then be inserted into a push-to-connect through-wall or tee fitting. This is the most common way to make the connection between microbore tubing and an experimental apparatus. The process for drilling holes in 1/4" plugs is as follows.

The first step in drilling a hole through a 1/4" plug is to hollow it out as shown below (apologies for the orientation, this is a problem with Confluence). The drill bit used in this photograph is 1/8". Any size smaller than the shaft of the plug and larger than 1/16" (the OD of the microbore tubing) will work. To drill this hole, it is important that the plug be fixed in a vertical position, which is what the drill vise is used for in this image. Also note in the foreground that there is a clamp holding the drill vise in place. This is to keep the drill bit centered on the vertical axis of the plug. The red tape on the drill bit is there to mark at what point the drilling should stop. If you drill straight through the plug with the large bit, you have rendered it useless. A good target to aim for is to drill to within 1/16" of the bottom of the plug and stop. That way, you won't have to thread the microbore tubing very far.

Once you've hollowed out the plug, the next step is to drill the small hole through which the microbore tubing will fit. The procedure is simply to drill with the smaller bit in the center of the bottom of the plug. If you hollowed out the plug correctly, you should not have to drill very far before you've cleared the material at the bottom of the plug.

Again, there is freedom in the choice of drill bit. The key constraint is that the hole provide an interference fit (i.e., it must be smaller than 1/16", the OD of the microbore). The other constraint is that it is not desirable to have a hole so small that it is nearly impossible to thread the microbore tubing through it. As you will have noticed if you performed the above steps for threading the microbore through a barb, it is actually a considerable challenge to fit the 1/16" tubing into the 0.047" hole in the barb. For this reason, a 0.052" (#55 wire gauge) drill bit was chosen so as to be tight-fitting, but not too difficult to thread through. These bits can be found in the drill drawer of the tool chest.

Pump Calibration

ProCoDA has a pump calibration routine available on the configuration tab. The pump must be on and running (controlled by ProCoDA) in order to complete the calibration.