The basic principle of the peristaltic pump traces back to human “peristalsis” [a term referring to the alternating contraction and relaxation of muscles around a tube to force the contents through it]. An elastomeric tube is squeezed along its length by rollers or shoes that pushes the fluid contained within. The tube’s restitution after squeezing produces a vacuum that draws fluid continuously into the tube. This creates a gentle pumping action that doesn’t cause any damage to the product. Contamination is avoided because the product is contained in the tube [the only pump part that comes in contact with the pumped fluid].
The peristaltic pump is a very versatile pump. It is a self-priming, positive displacement pump, able to deliver relatively high pressure, pass solids and transport corrosive and abrasive media. But selecting the right one for the job is important.
There are basically two types of peristaltic pump. Low pressure, low flow pumps that are commonly used in laboratories or for low flow dosing or metering applications and there are industrial class pumps. The industrial units are bigger, handling higher flows and able to generate higher pressures. It is these industrial pumps we will be concentrating on.
The peristaltic pump is easy to install and can be inexpensive to maintain if selected correctly.
There are a number of parameters that need to be considered when selection the right peristaltic pump for a particular application. These are: duty cycle; flow; pressure; suction conditions; the correct hose [tube] for the pumped media; temperature limitations; cleaning requirements [CIP or SIP]; the effect of possible contamination; and maintenance aspects.
Duty Cycle. It is important to consider the duty cycle when selecting a pump. If the pump is asked to operate on a continuous basis [hours on end], the speed must be reduced to prevent a shortened hose life. Good manufacturers will have performance curves that detail what part of the pump curve can be treated as continuous duty and what part should only be used as intermittent.
Flow. Most performance curves are based on water-like substances and flooded suction. When dealing with more viscous fluids or high suction lifts, this will need to be factored into sizing the pump for the correct flow inclusive of de-rating speeds for these aspects. Good manufacturers will have de-rating charts for increased viscosity.
Pressure. Not all peristaltic pumps were created equal. The better designs will enable pumps to be applied on applications with pressures to 15 bar. This is achieved through hoses rated to these pressures and rollers, rotors and other components designed for these high pressures. Manufacturers will detail what models are rated to these pressures and what the flow and speed limitations are.
Suction Conditions. Peristaltic pumps are capable of high suction lifts, but any peristaltic pump selected for a duty requiring a suction lift should have a pulsation dampener fitted. Also, if the viscosity exceeds 2000cPs, the suction line diameter should be increased. Another good “rule of thumb” is to keep the suction line as short as possible.
Correct Hose. Selecting the right hose material for an application is critical in achieving extended hose life, and also critical if hygiene is required for transporting food or pharmaceutical products. Some typical hose materials are as follows:-
- Natural Isoprene for abrasive fluids or moderately aggressive fluids. This is the most common hose material and is often available with various pressure ratings.
- Natural Isoprene with Substrate for Food Products. These hoses will have FDA approval numbers and be suitable for the transportation of food grade products. Should be able to sterilize with hot water and a diluted cleaning agent and also steam cleaning.
- This hose material is suitable for a wide range of chemicals.
- This hose is suitable for oils, greases, hydrocarbons and various solvents.
- NBR for Food Products. These hoses will also have FDA approval numbers and are suitable for oils and fats. Should be able to sterilize with hot water and a diluted cleaning agent and also steam cleaning.
- This hose is suitable for a range of concentrated acids and alkaline liquids.
- PHARMED Thermoplastc Elastomer Base Polypropylene. A limited use hose for liquid pharmaceutical products. Will have FDA approval numbers and should be capable of sterilization with hot water.
Temperature Limitations. Good manufacturers will have temperature limitations in their hose selection guides. Ensure operating temperatures do not exceed the temperature rating of the hose.
Cleaning Requirements. Where hoses need to be cleaned in place [CIP] or sterilized in place [SIP], the hose selection needs to allow for this. Also, it will be of great assistance to operators if pump rollers [or shoes] were able to be retracted easily to allow full flushing of the hose. Having this automated makes this process even simpler.
A pump with roller design, does not need casing lubricant
Contamination. If product contamination is an issue, selecting a peristaltic pump with rollers instead of shoes is best. The pumps with shoes will need their casings to be full of lubricating fluid. When the hose starts to fail, the lubricating fluid may contaminate the product being pumped.
Maintenance. A peristaltic pump does not require a lot of maintenance apart from hose changes. It is in this area that pumps with certain designs and certain features can save time and money. A pump with rollers does not have a casing full of lubricant, so does not need this oil drained and then re-filled again after the hose change, and no clean-up of the mess.
Early leak detection is another feature that reduces maintenance costs. This is only possible for pumps with the roller on bearing design. Because casings are not filled with fluid, a simple “plunger-in-cup” designed leak detector can pick up hose failures early, minimizing product loss and mess.
Leak detector is wired back to the control panel
A remotely operated retractable roller will also reduce maintenance costs by extending hose life. Between pumping cycles [over night, weekends, holiday periods], the roller can be retracted to remove pressure on the hose during these periods, greatly extending hose life.
A pump with remotely operated retractable roller system