Peristaltic pump (roller pump) is a type of positive displacement pump which works on the principle of peristalsis. It is useful for pumping a wide variety of fluids. For example, it is applicable in the machines of the pathology labs such as semi-auto biochemistry analyzer, colter counter, electrolyte analyzer, etc. Besides that, it is also useful in other equipment such as infusion pump, dialysis machine, Karl fisher titrator, etc. So here, we will be discussing the working principle of the peristaltic pump.
Besides that, we will also discuss the pros, cons, handling and calibration of the pump.
The working mechanism of the peristaltic pump is similar to that of the digestive system of the human body. The peristalsis mechanism causes the compression and the relaxation of the tube (or digestive tract) for the movement of the fluid particles.
The peristaltic pump consists of two parts. One of them is the tube/ hose and the other one is the rotor. The rotor consists of two or more rollers. The tube/hose goes around the rotor.
When the rotor rotates, the rollers will occlude/squeeze the tube. This will create a vacuum at the point of occlusion. The fluid will be sucked/trapped between the points of two occlusions. When the occlusion gets removed, the trapped fluid will get discharged.
Factors affecting the flow rate of the peristaltic pump
1. Pump speed
The output through the peristaltic pump is directly proportional to the speed of the pump. In other words, when the speed of the pump increases, the flow rate will also increase.
2. Internal diameter of the tube/hose
The flow rate is directly proportional to the internal diameter of the tube/hose. This means that the output through the tube is less than that from the hose. Hose, having a greater internal diameter, can be useful for higher pressure applications.
3. No. of the rollers
A rotor of the pump can have 2-7 rollers in it. The more is the roller in the pump, the more will be the occlusion of the pipe. More occlusion causes a decrease in the output of the pump.
4. Diameter of the roller
The flow rate is inversely proportional to the diameter of the roller.
5. Flexibility of the tubes
The tubes should be flexible for better output. So, stretchable tubes made up of silicone rubber, PVC, etc, are mostly in use for the peristalsis action.
The above statement holds as long as the pump speed is low. But when you increase the pump speed, the graph between the flow rate and those parameters will not be linear. Rather, the slope will begin to decrease.
Advantages of the Peristaltic pump
- There is no chance of cross-contamination. This is because only the interior surface of the tube is in contact with the fluid being pumped. So, the fluid will not come in contact with any other contaminated parts of the machine.
- Since the design of the peristaltic pump is simple, it is easy to handle and clean.
- It can handle corrosive fluids, highly viscous products, and shear-sensitive products (those products which may damage by the force applied, such as blood cells).
- A fixed amount of fluid is pumped per rotation. So it can be easily used for continuous mode. It has got a high precision.
Disadvantages of the Peristaltic pump
- Due to the continuous friction exerted by the rollers onto the tubes, there is a high chance of degradation of the tube. So, the tube needs to be replaced periodically.
- The flow of fluid is pulsed. So, it may not be useful for those applications which require a uniform flow of fluid.
When the roller of the pump causes occlusion of the tube, a vacuum is created. This causes the pulsating nature of the fluid. The increase in the flow rate, length of the tube, pump speed, and density of the fluid flowing through the tube are directly proportional to the pulsation rate.
Handling of the Peristaltic pump
- Always pay attention to the noise produced by the pump.
- You can clean the pump with ethanol.
- If there is any blockage in the pump you may even use a lubricant such as a grease.
- Check the tube that goes through the peristaltic pump from time to time. This is because there is a high chance of degradation of the tube in that area.
Before you do the calibration of the pump, you need to check out the condition of the pump. To do that, you can either check the pump speed or the flow rate of the fluid from the tube.
For checking the pump speed, take a stop-watch. Then count the number of rotations made by the pump in 15 seconds. Then multiply the obtained value by 4. This will give you the rpm of the pump. Now, compare the obtained rpm with the set value.
For checking the flow rate, take the fluid in a container. Now sip the fluid into the tube of the peristaltic pump. Then collect the dispensed fluid in a test tube from the other side of the tube/hose. Compare the obtained volume of fluid with the set value. But remember that, the flow rate depends upon the viscosity of the fluid flowing through the tube.
If there is no deviation between the set and obtained value, then that means the pump is working properly. Else you need to do the calibration.
Different machines or different models of different manufacturers can have different calibration methods. In some machines, you may need to do calibration by a trial and error method. In some other machine, you may follow the following steps
- Go to the calibration option in the machine.
- In the pump- calibration option set a suitable rpm or flow rate value.
- Then, turn on the pump and measure the same value of rpm or flow rate manually.
- When you reach the set value, turn off the pump.
- The mainboard will take this new reading as a standard value.
I suggest you, go through your user/service manual to know the method of pump calibration.