Flow vs Pressure ??

bgbrew01

New Member
I have been in a discussion with my partner and our PW distributer. Now I want to pose it to anyone out there who can help. I getting ready to buy four more machines but I am wanting something with a little a more kick to it. The two largest machines we are running now are 20HP honda's with general pumps. They are running 5.5 GPM @ 3500 psi. We are wanting to increase our performance. We concentrate almost exclusively on flat surface commercial concrete. I have been looking at General Pumps I can buy a EK18 that is 7.9 GPM at 4350 psi this would require a 25 hp motor. The other one we are looking at is a HD18 which will go 7.9 GPM at 7250 psi but it requires a 40 hp motor. What I am asking is will I get that much more performance out of the extra psi vs cost of the 40hp motor. Or will the increase in GPM and small increase in psi versus my older machines be enough?

Also, if anyone has seen any set ups similar to these (hot, belt-driven, electric start, skid mounts, etc). What kind of prices were they asking for them? I have not talked prices with this guy yet and I want to go him with a resonable dollar estimation.

One more thing, if have seen any set ups like these what brand and type of motor were they using? I know Hondas small motors stop at 20 HP and Briggs and Stratton's Vangaurds go to 22. Thanks alot.

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Hotwaterwizard

Guest
If you modify your existing units more GPM is not an option. Why? your burner only produces the amount of heat for your existing GPM. If you tamper with the flow your heater will not produce enough heat for that flow. The diameter of the coil is too small for the volume. If you have an 18 inch coil you would have to increase it to a 20 to 24 inch diameter coil and replace your fan and burner nozzle. My suggestion is to go with more PSI but what thickness is your coil. you may need to get a thicker walled coil. Say schedual 160 instead of schedual 80.

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Hotwaterwizard@aol.com If You have a problem with your machine, just ask me for help. Check out the Machine Problem Board
 

bgbrew01

New Member
I am not talking about modifying my existing equipment. I am planning to have some totally new equuipment built and having the coils and everything else matched to the psi and flow. I am really just wandering if the increae in psi is just an overkill if I increase my flow by ~2GPM. Or if spending the money in difference between the 25 and 40HP motor is worth it.

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Hotwaterwizard

Guest
I don't think the difference is worth the cost. You will have extra cost in, Special hoses, special unloaders, special trigger guns, higher fuel cost, ect, ect, ect. Just my opinion.


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Hotwaterwizard@aol.com If You have a problem with your machine, just ask me for help. Check out the Machine Problem Board
 
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PressureWasherZoneDoctor

Guest
In my 20 + years of experience, in the pressure washing industry, I have found that FLOW / GPM, is all to often discounted.

For flat surface cleaning, sidewalks, buildings, etc.
"In my opinion" increasing GPM from 5GPM to 6, 7, 8, or more would be MUCH more BENEFICIAL than increasing pressure, even if you drop PSI from 3000 to 2000 PSI but add GPM you will be ahead!

Do you really need 210 degree water for your cleaning application?

A pressure washer set up for lets say 7 GPM @ 3000 PSI but equipped with a burner / coil for a 5 GPM unit will still give you Hot Water ( just not 200 degrees) however you can bypass some of that 7 gpm, by installing a valve and have 5 GPM at 200 degrees available when temperature is more important than volume.

There are as many different schools of thought on this issue, as there are different makes of pressure washers, this just happens to be mine.

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RX@easycleansystem
s.com www.easycleansystem
s.com

[This message has been edited by PressureWasherZoneDoctor (edited September 10, 2000).]
 
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Hotwaterwizard

Guest
You are right Mark. As a distributor of pressure washers like me, you also know the difference in the cost of a higher volume machine. Put yourself in these guys place is it worth the double or more price tag for the bigger machine? For us the sale would be a nice fat wallet. But, I am trying to give an honest opinion without my wallet in the picture. They could buy two 5305 Alkota machines for the cost of it's larger version.

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Hotwaterwizard@aol.com If You have a problem with your machine, just ask me for help. Check out the Machine Problem Board
 
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Hotwaterwizard

Guest
Please don't missunderstand my last post. I am not trying to say that anyone is trying to make their wallet fat. I'm just trying to say the manufactures have a big jump in their prices of machines with higher volume. Also higher volume is a great thing if you can afford it. Just make sure the water source is big enough to supply water to that size machine. You may have to tap into a fire hydrant everytime you want to use the machine for high volume.
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Hotwaterwizard@aol.com If You have a problem with your machine, just ask me for help. Check out the Machine Problem Board
 

JT

New Member
It may be of interest that the effects of GPM vs. pressure can be quantified by the following formula (given in Journey's Universal Guide to Pressure Washer Repair):

Force of impact = Nozzle constant x GPM x square root of pressure.

Force of impact (in pounds) is essentially cleaning power.

Nozzle constant is a small constant (that I can't remember exactly, but is something like .05 or .06), the exact value doesn't matter if you just want to compare the effect on cleaning power of various pressure/GPM values.

This equation bears out ZoneDoctors experience i.e. that an increase in GPM is more important than an increase in pressure.

As an example, start with a 4 GPM @ 3500 PSI unit (assuming a nozzle constant of .0625)

The water impact at the nozzle tip would be:
.0625 x 4 x 59.16 = 14.79 lbs (sq root of 3500 = 59.16)

A unit with 4 GPM @ 4500 PSI would produce:
.0625 x 4 x 67.08 = 16.77 lbs, a 13.39% improvement.

A unit wiht 5 GPM @ 3500 PSI would produce:
.0625 x 5 x 58.16 = 18.49 lbs, a 25% improvement.


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Mike Taylor

New Member
Hello. I have 2 machines, one is 8.5 gpm @ 2500 psi. That has a 20 hp Onan Motor (not sure of the pump) It ran me about 1400 used. The other does 5.5 gpm at 3000 psi. It has a 13hp Honda and a cat pump. It ran me about 1000 used. The bigger one by far smokes the small one. I do alot of commercial flat work as well as residential and the extra GPM makes alot of difference. I dont use Hot water yet, but am thinkin about it. Alot of the guys I talk to in my area agree that GPM is better than pressure. Good luck whatever you decide, hope this was of some help
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PS the big machine is Belt drive and the small is direct drive.


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Always Under Pressure Inc Mike Taylor Pompano Beach Fla USAps the Big machine is belt drive and the small is direct.ps the big machine is Belt drive and the small is direct drive.

[This message has been edited by Mike Taylor (edited November 30, 2000).]
 
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Hotwaterwizard

Guest
Check out General Pump Model 5050 5gpm at 5000psi

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Hotwaterwizard@aol.com If You have a problem with your machine, just ask me for help. Check out the Machine Problem Board
 

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