Small Engines (Lawn Mowers, etc.): Coleman 1500 PSI pressure washer, triplex plunger pumps, psi pressure washer

Question
Hi.  I have a Coleman 1500 PSI pressure washer.  Model PW0811505 with a Tecumseh Motor.  About 10 years old.  The unit is not building up pressure.  The motor runs, water comes out the wand, but not at very high pressure.  I have taken it apart, confirmed that the shaft of the motor is turning.   Took the pump housing off, confirmed that the pump mechanism looks to be working.  I can see the 3 'pistons' moving up and down.  I cleaned and oiled everthing.  On the unit, there is a plae where the water goes out into the wand house.  On the opposite end of that is a black plastic plug.  The threads on that plug have been stripped by corrosion.  I got a new 1/2 in, machine thread plug from the hardware store and it fits.  But I am wondering, inside the chamber the plug goes into is a cartridge and a spring.  I suspect the pistons move up and down to create pressure and that cartridge and spring have a lot to do with it.  My question is, does anyone know exactly how the unit builds pressure, what this cartridge and spring have to do with it, and if it is imperative that I have exactly the right plug in there?

Answer
I got this information off how stuff works.com. There usually a pretty good source of information. When you need to know something. After reading your text I believe the answer is in here and is a nozzle problem of filter problem or trigger problem


Here Is the Information
High pressure pump

You've now arrived at the "core" of the system, the high pressure pump. All are positive displacement reciprocating pumps either piston or plunger types. Plunger pumps are the most efficient and have a longer life, therefore they are the most commonly employed pumps found on a quality power washer today.

There are duplex and triplex plunger pumps. Plungers are typically made of ceramic, a very hard material with excellent wear resistant charachteristics. The triplex pump has become the most popular due to the smoother flow it creates.

These pumps are incredibly robust and virtually trouble free when properly maintained. Most people suspect the pump first when experiencing a problem but amazingly 90% of problems can be traced to causes other than the pump.

THE UNLOADER VALVE

This is the main "safety" in your power washer system. The most commonly used is the "pressure actuated" type valve. When the pressure gun trigger is released the valve senses the pressure build up and like a "traffic cop" it diverts the water flow from the pump outlet back into the inlet side of the pump this is called "bypass mode." Without this critical component this closed-gun situation would build pressure to the point where it would stall the power source, rupture the gun, hose or even the pump itself.

High PRESSURE HOSE

A high pressure hose is composed of an inner tube in which the water flows. This is wrapped in either a single or a double braid of wire mesh. This is in turn surrounded by a rubber outer cover. The cheaper hoses are covered in a thermoplastic material the better hoses have rubber covers.

Most hoses are manufactured with burst ratings 4X their rated working pressure. When matching hoses to machines try to use a hose rated slightly higher than the psi rating of your machine. It will last longer. Typical psi ratings are 3000psi, 4000 psi ,4500 psi, 5000psi and 6,000 psi. 3,000 and 4.000 psi hoses are generally single braid while 5,000 psi and above are virtually always double braided (2-wire).
Trigger guns that stop the water flow are the most commonly used guns in power washer systems equipped with unloader valves. Front entry guns are common on the lesser priced units and rear entry guns are far and away the most popular. Rear entry guns do a better job of keeping the hose out of the operators' way and are better balanced.These guns control the water flow via a spring, ball and seat which are actuated by the trigger. When the trigger is released the ball is pressed against the seat by the spring and water, aided by a check valve in the outlet of the unloader. Water is "trapped" in the hose under pressure and the pump enters bypass mode. With this setup you will experience some "kickback" when you squeeze the trigger so be careful when using ladders and other types of access equipment.



HIGH PRESSURE NOZZLES

The high pressure nozzle is a much more important component to the power washer than most realize. This creates the restriction that allows the water flow to become "pressurized" and delivered with such force. A worn nozzle will reduce pressure noticeably. A mismatched orifice can have the same effect. A nozzle with little to no wear and one with an orifice properly sized to your pumps' output will get the most performance from your machine.