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Soap injection rate at pump

I have Dwyer flow meters and draw both soap and wax at 10 oz's a minute into the pump. Then *tip* the hydrominder accordingly. At 3 gpm water flow, that's about 2.6%. It works well for me. Plus it's a lot less cycling on the hydrominders. I've had my new hydrominder tanks and solenoids installed almost 2 years. I Haven't had to make one flow adjustment since the installation.
 
The reason I was asking.....

I have been playing around with different ways of plumbing my pump stand. I'm going to completely redesign and rebuild the stand this winter. I have a Dosatron that I have been playing around with. Had an idea of pressure feeding the high pressure pump with city water pressure dialed down to approx 30 PSI. Then using the dosatron to inject the soap / wax into the inlet side of the pump at 40-50 PSI. No Venturi injector, tank, hydrominder......
Thoughts ?
 
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I went through this same exercise about 2 years ago thinking I needed to get away from float tanks....But came to the realization that a city pressure system had its own set of issues, just like all systems do. So I decided against it and go the lesser evil route..... I installed Erie solenoids on the hot/cold water supply tee'ing in soap and wax. Soap and wax are hot water and rinse is cold. Cold/hot supply tubing is 1/2" and no need to install valves to restrict water flow to the pumps so they draw soap/wax. This has proven to be a flawless setup for over 2 years now. I use Kip SS solenoids with built in metering screws. Have never touched them since they were installed. Pretty simple actually.

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We lower our incoming water pressure down to around 20 psi with Generant GE4HC-375B regulator on every pumping unit and use a DEMA 203C injector to inject the Soap and Wax. We’ve been doing this for over 30 years with very few problems. I’ve thought about using the Dosatron but the operators who I know who have them haven’t been very happy with them. One thing about lowering your incoming water and pressure feeding your high pressure pumps, you’ll never have a head wash out, my pumps are over 30 years old and still going strong.
 
Two years ago when I was trying to figure out which direction to go, Randy took the time to explain his system to me and send me tons of pictures. I went as far as ordering a Dema Injector and pressure regulator to test. It worked exactly as Randy described….But…I just couldn’t bring myself to rely on either the hot or cold solenoid to open to feed my pumps.

With 35 years in Manufacturing and Engineering, I try to build “Fail-Safe” systems whenever possible. That’s why I decided to go the Erie valve and float tank route…. For those that don’t know, The Erie valve is a motorized valve that is either normally open or normally closed depending on which way you feed the hot/cold supply. A Heavy spring returns the valve to closed position when de-energized. I opted to have the hot feed come in on the normally open side for soap and wax (Not energized). Most customers select soap first, so the Erie is in the correct feed position for hot soap…No delay…When rinse is selected, the solenoid is energized and switches to cold water. Switch over takes about 8-9 seconds. Hardly noticeable to the customer and no negative affect.

Every time I wash a bay out, I am basically testing the solenoids. The water starts out warm on rinse and quickly changes to cold water. If it fails to turn cold (Which has never happened in 2 years!) I will know the valve has failed. Worst case with a failed valve, customer gets 100% hot water for all cycles. Not a bad thing. Another upside, it’s physically impossible for a non-working Erie valve to starve a pump. The “Fail-Safe” part I designed into my system. But then I have float valves! Pick your poison!
 
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