Thursday, January 10, 2013

Gallons Per Minute gpm

I guess I had mentioned GPM or gallons per minute right along and had not really explained it. To correct my mistake I will now explain it.  It is a easy concept, how many gallons can you fill up in the elapse time of one minute. Most pressure washer will be in whole numbers but some are rate to the nearest half such as 4.5 gpm or 5 gpm. Remember the formula to figure CUs? Your total CU "cleaning units" CU=PSI x GPM is the most important factor in the rating of a pressure washer, but how can you get those gallons running thru the pump we will discuss the plunger pump because it is the most widely use pump on the pressure washer. By having 3 cylinders we can pump more than just 2 so how many cylinders or plunger are moving inside we can push more water thru. Most professional washers us the triplex pump a pump running 3 plungers most pay for time car washes use twin plunger pumps less pressure and one less plunger that needs service. If you go to the "big box store" and look at the pumps either underneath or beside the motor you will notice the size is any where from the size of your fist to that of a half gallon of milk. On the professional models the pump is about the size of a shoe box and then go up in size the largest I have seen in person was over 16+ inches wide about a foot high and 2 feet long.

Industrial pressure washer pump

This is what most professionals will use
Medium sized residential power washer

Small pump use on electric units as well as smaller gas motors

Why so big? because we can make those plungers bigger and inturn you will run more water thru the pump with each stroke of the plunger the bigger area will force more water thru. When I started in the business 5 gallons per minute was just about the best you could do why would you need more? The size of the plungers is the best way we can add more gallons per minute and with larger amounts of water will change our CU  an example of this is 3000 psi pump putting out 5 gpm 3000x5=15000 cleaning units 3000 psi pump putting out 10 gpm 3000x10=30000 cleaning units and so on 8 and 10 gpm pumps are getting more popular to day now this type of power in the hands of a untrained person can cause real damage remember the highest powered washer is not always the best. Why use such a thing then you can run two wands or guns off of one unit two people using the same pump will each have 3000 psi and can use 5 gpm at the same time saving water and getting the job done quicker. The use of a surface washer also requires larger volumes of water I will talk about these when we discuss attachments later. Simply put gpm is how much water a pressure washer can put out.

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