Everything should be made as simple as possible, but not simpler.
When it comes to simplicity, peristaltic pumps take the cake. If you've ever squeezed a tube of toothpaste from the bottom, you have a basic understanding of how peristaltic pumps work. There are no gears, seals, check valves, or impellers. It's just hose inside. That makes them simple to use, simple to work on, and simply amazing.
Peristaltic pumps are everywhere. In fact, I can guarantee that you use a type of peristaltic pump hundreds of times a day. The act of swallowing induces peristalsis in your esophagus, which pushes the food down into your stomach.
For many processes peristaltics are considered the "Cadillac" option because of how gently they're able to handle materials, while at the same time pushing them over great distances. However, while they're growing in popularity, we've still seen some confusion about how they work and what they're capable of.
How Do They Work?
As with most pumping principles, it's easier to see how a peristaltic pump works than it is to try and describe it.
In the above animation, the blue tank represents the source of liquid. Inside the pump is a hose. The two white rollers on either end of the rotor roll over the hose, squeezing it each time they pass. As the rollers pass over the hose, it springs back into place. This creates vacuum at the inlet, which pulls material in to be pumped.
Pretty simple, right? Again, it's just like squeezing a tube of toothpaste. This peristaltic motion is ideal for sensitive liquids because there is no shear whatsoever. It's also great for abrasive or aggressive liquids because there are no valves or other obstructions within the pump. It's just hose inside, nothing else.
As a result of their ability to handle both delicate and abrasive materials, peristaltic pumps are used in many applications. They're used in hospitals to pump blood during open heart surgery. Blood is particularly delicate, so this is a great indication of just how gentle peristaltic pumps are. They are also used for moving rock slurries in mining, and even viscous, abrasive materials like bentonite.
What Are They Good At Pumping?
As mentioned above, peristaltic pumps are good at pumping just about anything you can think of. Products that would normally be considered too aggressive or corrosive to pump are no problem. As long as the material of the peristaltic hose is compatible with the product you're pumping (and hoses are available in many different compounds), you're good to go.
In strictly mechanical terms, they are the most gentle pump. In addition to not exhibiting shear, they are also able to rotate very slowly relative to other types of pumps, meaning less disturbance overall. For example, to pump 50 GPM a peristaltic pump like the Ragazzini MS2 appropriately only has to make a few dozen revolutions per minute. Similarly-sized RPD pumps usually have to make hundreds of revolutions per minute to achieve the same flow rates.
Peristaltic pumps are also great for solids and semi-solids. The largest peristaltic pumps we sell can pump whole clusters of grapes over hundreds of feet. A peristaltic pump with hopper is a great catch basin for the outlet of a sorting table, optical sorter, or mechanical sorter. It can pump the grapes directly to your tank. Once they're fermented, you can pump the fermented must directly to your press.
Customers who use Waukesha RPD pumps often contact us looking to improve their must pumping processes after they find that Waukesha pumps can be brought down in no time if a hard solid is accidentally introduced. Miniscule pieces of stray vineyard staples and ties, or errant tri clamp fittings accidentally dropped into the hopper of a Waukesha can bring harvest processing to a screeching halt, quite literally. The peristaltic, on the other hand, just pushes it through.
What Aren't They Good At Pumping?
Since the interior of a peristaltic pump is just hose, they tend to have the same limitations that hose does. Temperature and chemical compatibility may be an issue if you're pumping extremely hot liquids. Likewise, if you're pumping aggressive or corrosive chemicals, you should ensure that the chemical is not reactive with the peristaltic hose material. As mentioned previously, peristaltic hoses are made in a variety of different compounds, so it's usually not difficult to find one that's right for your application.
What To Look For In A Peristaltic Pump
We sell peristaltic pumps manufactured by Ragazzini in Faenza, Italy. Our feeling– backed by decades of experience and testimonials from happy customers–is that Ragazzini makes the best peristaltic pumps in the world, bar none. The most enthusiastic Ragazzini customers we've found are ones who've tried peristaltic pumps made by other manufacturers and then discovered Ragazzini. Time and again we hear that the other brands don't have the same power, thoughtfulness of design, and attention to detail that Ragazzini offers. Given the simplicity of the peristaltic principle, it may be surprising to find that making a good peristaltic pump requires considerable thought and well-executed design. So, here's what you need to look for in a peristaltic pump:
Full tube occlusion: This means the tube inside the pump should be fully closed by the rollers when they pass by. If the tube is not fully closed there is an opportunity for "slippage", where material remains in the tube as the rollers pass by. This drastically reduces the pump's power and throughput. Still, it is difficult for lesser-made peristaltic pumps to achieve full tube occlusion, so many don't.
Body construction: Given that the rollers should be fully closing the tube, a lot of force is being applied to the sides of the pump each time the rollers pass by. This means the body of the pump shoud be able to withstand a lot of pressure without bending. Ragazzini's pumps are made from thick cast metal. We see a lot of peristaltic pumps made from stainless steel sheet metal. This is not optimal, as sheet metal is much more prone to flexing. In turn, this leads to reduced power as force is absorbed by the body flexing. The Ragazzini's thick cast metal body remains solid throughout. As a result, Ragazzinis are capable of moving products over long distances, and at very high pressures, if necessary.
Tube design: The tube in a peristaltic pump has to withstand a lot of punishment. It is constantly being squeezed, and must immediately spring back to its original position so that it can pull adequate vacuum. Ragazzini's peristaltic tubes are composed of four layers. The outer layer provides a tough, smooth surface for the rollers to contact and glide against. The next layer provides woven reinforcement to ensure the tubes longevity and integrity. The third layer is thick and springy with excellent memory to return to its original shape. The final layer comes into contact with your product. All of this thoughtful design ensures that tubes last a long time, which is great since they're the only part of the pump that is considered a true wear part. On average Ragazzini's tubes last 3-5 years with normal use, and much longer if they are only used intermittently.
As mentioned above, the tube is the only wear part on a well-designed peristaltic pump. Therefore, maintenance is simple. Simply lubricate the tube regularly. Ragazzini recommends adding 5 oz. of grease every 100 working hours. If you use your pump 3 hours a day that's about once a month. If the pump will be out of use for extended periods of time, you should remove one of the rollers to allow the tube to rest and retain its original round shape. That's it! Peristaltic pumps are perhaps the lowest-maintenance pumps you can purchase.
Because of their gentle handling and ability to move large solids effectively, peristaltic pumps are regarded as the best pumps for moving must, grapes, and even whole clusters. But not all peristaltic pumps are created equally. Let us know if you need help or advice selecting a peristaltic pump for your facility.