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What is the Difference between Plunger Pumps and Piston Pumps?

Choose the Right Pump for Your Pressure Washer

Are you going to be using a pressure washer for high-pressure applications? Blasting oil and fats off concrete or brick walls? Removing graffiti from the outside of your building? Cleaning your industrial machinery?

Or maybe you’re going to be using a pressure washer for lower-pressure applications? Washing the sides of your house? Washing the family car? Washing the mud off your kids in the backyard—okay, that one is probably a criminal act, so don’t do it. Soft washing your roof?

Different types of pumps have different applications they work best for. The text below describes the differences and similarities between types of pumps, and the different applications each is best suited for.

There are chiefly two types of pumps used in contemporary pressure washers: plunger pumps and piston pumps.

Similarities between Piston & Plunger Pumps

For the most part, these two types of pumps function the same way. Both are reciprocating positive displacement pumps which pull water through an intake valve and into a chamber and push it—pressurized—back out through an outflow valve. These valves are engineered to be one-way only, meaning the intake valve will only open under negative pressure and the outflow valve will only open under positive pressure.

Most pumps, both plunger and piston type, are either duplex or triplex variants.

Duplex pumps have two pistons or plungers while triplex pumps contain three. This means duplex pumps must move faster to generate the same pressure levels as triplex pumps, consequently wearing their parts faster, and often causing a pulsating effect.

Triplex pumps last longer because each individual component has to do less work. Furthermore, the flow of water from triplex pumps is more constant, lessening the components’ strain even more.

How a Plunger Pump Works

Plunger pumps use a reciprocating plunger to pressurize water and force it through the outlet valve. The plunger is normally made out of hard ceramic, which is very durable and resistant to wear.

The plunger is attached via connecting rod to a rotor. As the ceramic plunger reciprocates out, it creates suction pressure drawing fluid through the intake. As the rotor turns, the plunger is pushed back down to send fluid through the outflow valve.

The pump’s high-pressure seal remains stationary, allowing plunger pumps to be used at much higher pressures than piston pumps.

How a Piston Pump Works

Similar to plunger pumps, piston pumps use reciprocating pistons to pressurize water and force it through the outlet valve. The difference between a piston and plunger pumps is the high-pressure seal. In a piston pump, the seal is attached to and reciprocates along with the piston.

Because of this, piston pump seals wear out faster and cannot handle as much pressure compared to plunger pumps. As the seal wears out, the power washer will suffer from reduced pressure buildup, resulting in a weakened stream and inefficient operation.

Diagnosing Pressure Washer Problems

Pump failure is rarely the cause of power washer problems. The leading causes of pressure washer problems are system restrictions, which cause the pump to fail.

If the inlet hose or valve is not getting enough water to the pump, air is sucked in—this is called cavitation. When this mixture of water and air bubbles is pressurized it creates small explosions, damaging the pump and its components.

The easiest way to combat cavitation is to install a quality inlet valve and filter. This is especially true if the inlet source is a water tank, where many larger particles may sit and settle. If you are using particulates, such as sand, to assist with surface cleaning, make sure to use an appropriately-sized filter mesh to prevent clogging; you must also make sure your pressure washer has enough power to make sure the sand does not wash back into the machine, whereby ruining the pump.

Stuck? Let The Power Wash Store Solve Your Problems

There are tons of possible causes to explain your pressure washer pump problems—cavitation being the primary cause.

Other causes include (but are not limited to):

  • Scratched, scarred, or damaged piston/plunger
  • Cracked or worn packings
  • Abrasive materials in the pumped fluid
  • Too high of temperature of pumped liquid
  • Broken or cracked crankshaft

Taken care of properly, with regular maintenance checkups, your pressure washer pump should last at least as long as the hour-rating it’s supposed to last for as per the owner’s manual. As we’ve said, actual pump failure is rarely the cause of the problem, but rather the result. Give us a call or submit a contact form with your questions, and we’ll do our very best to give you the right answer.

Contact The Power Wash Store's customer service representatives to have you questions answered today.