What Is a Positive Displacement Pump?

It came out in May that the worldwide market for positive displacement pumps is forecasted to reach $11.25 billion in the next seven years. That’s almost double the market’s value in 2019. Why are these pumps high in demand? What’s driving the increased need for this specific type of pump? There are several factors.

It helps to understand what positive displacement pumps are used for. They remove liquids from discharge pipes. They’re useful in many industries including wastewater, food and beverage, oil and gas, mining, etc. If you have liquid or fluid matter that needs to be moved from Point A to Point B, a positive displacement pump is your answer. Take a closer look at how these pumps help in these industries, what you should look for, and how they work.

A Guide to How Positive Displacement Pumps Work

Pumps move liquids or fluid materials from one area to another. There are axial-flow pumps fluids in one direction. Liquids come in passes through an impeller and travel out the other end. A centrifugal pump changes the flow by using a motor and impeller to create energy that pushes fluids along. The final option is a positive displacement pump that captures an amount of fluid and forces it into the discharge pipe. The benefit is the pump handles a constant volume even if the pressure changes.

These pumps are categorized by their mechanisms:

  1. Linear-type: Chain or rope pumps
  2. Reciprocating-type: Diaphragm, piston, plunger, or radial piston pumps
  3. Rotary-type: Gear, hollow disk, rotary vane, screw, or vibratory pumps

A linear-type of positive displacement pump uses a chain or rope and some form of a plate or even bucket to displace liquids. Go back in time to an ox-powered water wheel. Oxen were tethered to the big wheel and walked in circles. That motion moved the wheel, which moved the chain or rope along a pulley or up and down a drilled or dug well to collect water from deep within the well. Back up at the surface, the motion at the top of the pulley system dumped the water into a discharge chute while the buckets made a new path. Today, they’re more likely to have a chain and disc system that fits within a tube or pipe. As the discs are pulled up through the tube or pipe, water is trapped and is drawn upward.

Next up is a reciprocating type. How it works depends on the type. Think of the old-fashioned well pump. People pumped the handle and each upward pull of that handle drew water up to the discharge pipe. There’s also a piston pump that also uses the upward pull or downward thrust to move liquids. A diaphragm pump is the other type of reciprocating pump. An air bladder (diaphragm) moves up to decrease pressure or down to increase pressure. If you have a private well, you have a pressure tank that helps water flow from the well to the different water lines within the home.

The final main type of positive displacement pumps is the rotary type. There are five types of rotary positive replacement pumps: gear, hollow disk, rotary vane, screw, or vibratory. Screw pumps are one of the types of pumps you’ll encounter a lot in water treatment plants, which makes them one of the more familiar types. You can have an open or enclosed screw pump. They work by having a giant screw within a closed or open chute or pipe. The blades of that screw capture the fluid from a lower pool of liquid, and the motion of the turning screw propels it upwards and to the top of that chute or pipe.

Screw pumps are popular in so many industries and settings. It’s worth stopping to talk about them. You have open and closed. Open is in a concrete trough, and enclosed is in a steel tube. For enclosed screw pumps, there are the Type C or Type S. Type C pumps have two flights (screws) that are welded into the rotating tube. Type S works oppositely with a stationary tube.

While the mechanics vary, the goal of any pump is the same. The mechanics draw in the fluid material on one side, move it through to the next with the help of motors or human or animal power. For the most part, you’ll be relying on motors to power these pumps. If energy-efficiency is vital to your water treatment plan, home setting, or business, you should look at solar-powered or wind-powered electricity to run your pump.

Their Role in Different Industries

That’s the breakdown of the different types of positive displacement pumps. How are they used in different industries? Getting back to the increased need for positive displacement pumps in the next seven years, a driving force in this is going to be the need to find new options for energy. Natural gas is in high demand and is just one of several hydrocarbons that are drawn from the earth using positive displacement pumps. Because drilling and fracking require a lot of pressure, piston pumps that handle the high-pressure situation are often used.

As some look for environmentally-friendly ways to heat their homes and businesses, hydrocarbons aren’t the first choice. Solar and wind power are one choice, but there’s one that is gaining popularity. Geothermal energy needs powerful pumps to move the water from below ground into the building.

You can use these pumps in a geothermal system. Geothermal energy takes the natural warmth found within the earth and uses it for home heating. You pull the warmer water from deep within the ground where it releases that warmth into the house and discharges the cooled water in a continuing cycle. In the summer, geothermal energy helps keep the house cool. The surface temperature is warmer than the temperature deep in the earth. The cooler water is drawn into the home to cool the air and discharges the warmer water back in the ground to cool again. A positive displacement pump can help keep that flow of water from the underground to the building from coming to a stop.

In water treatment, these pumps move the wastewater from the sewer lines or septage station to the next steps in the treatment process. Screw pumps are the common option in a waste treatment plant. If solids like fat balls or fecal matter won’t mess up the screw pump. They’ll move to the next steps where the sludge is separated for processing. Sludge eventually ends up in disposal tanks where it can be dried and composted or taken to a landfill. More homes and businesses mean more of a load. To meet the increased load, water treatment plants are upgrading and increasing capacity. They’re adding energy-efficient measures to lower overall costs. This all starts by choosing the right pumps and water treatment equipment.

In a rice paddy or other agricultural settings where irrigation is needed, positive displacement pumps move water from another water source to your fields or rice paddies. In rural settings, a tractor may be attached to a chain using a chain pump. In a large commercial field that grows everything from corn to wheat, irrigation systems need to be efficient and move a lot of water every day. These settings may use screw pumps to move water from a lower pond or water tank to the elevated fields. Liquid manure needs to be pumped into trucks for spreading.

Pumps also serve a need in the food industry. A plant that makes sausage needs a way to pump the mix of ground meat and spices into the machines that fill casings. A viscous mixture like pasta sauce needs to be transferred from the vats where it’s cooked into machinery that jars it. Food grade screw pumps do this without breaking down as the acidic sauce passes through the pumps for hours at a time.

How Do You Shop for a Positive Displacement Pump?

What are your needs? Archimedean screw pumps don’t clog and can move the liquids and solids wastewater treatment plants handle. Screw pumps are used in sludge pumping, effluent lift stations, and stormwater management. They can help drain land or move water from a water source to elevated fields. Screw pumps are used to move grain in an agricultural setting. They’re also helpful in moving liquids around in wineries and breweries. While your budget is important, it’s also important to have a clear vision of what the pump will do. Do you need the pump that can process foods or one that will be exposed to the outside elements?

You also need to have a clear idea of where the pump is going so that you get the right size. An enclosed screw pump takes up less space than an open screw pump. A Type S screw pump may take up more space because it has a pivoting end. The pump needs to keep up with the flow rate without causing a backup. How much space is there? If there are space limitations, you need to choose a pump that is the right size for the space you have.

Maintenance is the third factor to weigh carefully. Motors in a pump need to be lubricated or they’ll seize. Some units are designed to be maintenance-free, others require a little more care. How much staff and/or time do you have for upkeep? Do you want to make sure bearings are lubricated after months or years of use or do you prefer the idea of self-contained lubrication that is always there? A Type E Sealed Bearing requires little to no maintenance, and if re-lubrication ever is needed, it’s not time-consuming as you never have to remove the bearing.

Do you have time to clean the components, or should the pump be designed to prevent clogs or build-up? A clog-free design is one of the factors that make Lakeside Equipment’s screw pumps the best choice when it comes to maintenance and cleaning. Screen rakes also help keep trash from getting to your equipment.

Choose a specialist in water treatment and hydropower equipment. Lakeside Equipment’s expertise dates back to 1928. We make sure your goals are met by talking about your budget, space, and district. If you’re in an area where the population growth is rapid, a design that considers that growth is important. If you’re looking for equipment that cuts electricity costs, we can help there, too. Give us a call to learn more about Lakeside’s positive displacement pumps.