There are a number of ways your pump can get damaged.  There are also a number of ways to protect your pump from these hazards.

Your first line of defense to protect your pump is to ensure your water supply is clean.  If debris enters the pump you could be faced with cracked or scored plungers, prematurely worn seals, worn or cracked valves, broken valve springs, scored pump cylinders, plugged unloader valve and plugged nozzle.  A myriad of problems that can be prevented with a simple inexpensive water filter.

So, you are working 50 feet away from your machine and you need to move something out of the way or the neighbor wants to ask a question.  What do you do?  Lay the wand down and move that thing out of the way or carry on a conversation over the fence.  If it takes more that a few minutes your pump may have experienced serious damage, due to overheating, by the time you pick up your wand and go back to work.

Heat is your pump's biggest enemy and your pump generates a lot of heat  Your pump turns at a great rate.  Most run between 1700 to 3400 times per minute!  Manufacturers design pumps to be cooled by the incoming cold water, which picks up a small amount of heat on it's way through the internals and out the discharge (nozzle).

By closing the trigger you stop the water from going out the discharge but you pump is still creating heat......with no place to go.  Your pump is positive displacement design. When you shutoff the trigger gun the water continues to be pumped.  The unloader valve is designed to redirect the flow from your hose to the inlet side of the pump.  This solves the problem of where the water goes but creates a problem of the heat generated has no place to go.  Hence, the water heats up, potentially destroying your pump.  Water in the head of the pump can heat up to the boiling point, cracking pistons, melting seals, warping the head melting orings.  Time for a new pump!

What to do?

  1. Never leave the pump on bypass for more than a few minutes.  
  2. Shut your machine off rather than leave it on bypass. 
  3. Pull the trigger once in a while to cool the pump with fresh, cold, water.
  4. Ensure you pump has a thermal relief valve which is designed to open, and let cold water in, at approximately 140 degrees F.  Don't rely on this valve too often.  Once your pump reaches the open temperature your pump seals may already be somewhat damaged.  Accumulation of seal damage will eventually ruin the seals.  Also, some thermal relief valves are a one-time disc design, so once they open they are done and need replacement.
  5. Run your bypass water to the ground or a drain.  This is a very effective method, especially for those working a long distance from the machine.  Water goes through the pump, taking heat with it, even when the trigger is released.  It's a fairly simple procedure to do but you need a pump with an external bypass.  Pumps with internal bypass can not be converted.  Pumps with external bypass will have a hose running from the pressure side of the unloader to the inlet side of the pump.  Simply remove the hose from the inlet, seal the inlet with a brass plug, tie the bypass hose to the machine so it won't fly around and your done.  You can put a garden hose fitting on the bypass hose which makes it easy to run bypass water to a drain or garden area.  If water consumption is of a concern in your area you may want to consider the extra water consumption as a concern.  This type of bypass set up is ideal for any system drawing wash water from a tank as no bypass water is wasted, it's simply returned to the tank.