Weep water check valve question

[1carwash1]

Is it really necessary to install a check valve so that weep water does not flow back through the pump head to the gravity fed storage tanks? I was having a conversation with a fellow operator and he said the pump valves will not prevent the back flow of weep water. I once had a wash where the weep water was fed directly to one output port and it only had a check valve that prevented the high pressure water from backing up the weep line.

 

[I.B. Washincars]

Yes and no. Sometimes the valves may hold it back, but in my experience, I needed a CV. If your holding tank is large, it may be backing up and you don’t realize it because it doesn’t run over.

 

[MEP001]

Ideally you don't need a check valve to keep the weep water from backing up through the pump. Some of my bays have no check valve on the pump inlet because I've just been removing them as they fail and I removed the rinse solenoids after the freeze last year so there's no need for the check valve. I don't have any issue with weep backing up through the pumps, but I keep on top of pump maintenance. It's usually the valves in the pump that allow backflow since they don't always seat 100%, but I test and replace them if they don't.

 

[1carwash1]

Thanks! How do you go about testing the valves (Cat 5CP2120)?

 

[MEP001]

Suck on them.

 

[1carwash1]

Suck on them.

LOL, You must be kidding!

 

[sparkey]

I have noticed in the past when my check valves would go bad on a slow day my tank would sometimes overflow from weep water backing up through the pump.

 

[MEP001]

LOL, You must be kidding!

Nope.

 

[2Biz]

I think you will find the cv also keeps water from siphoning out of the float tanks if you don't have a cv between the tank and pump. I have Giant regulators/unloaded that have a built in cv for both weep and siphoning.

 

[MEP001]

I have Giant regulators/unloaded that have a built in cv for both weep and siphoning.

The check valves are there because they're unloaders. They're meant to be used with full shutoff guns, and when the trigger is released the pressure is trapped in the hose and the regulator "unloads" the pressure from the pump so it runs with no load on the motor. They're mainly meant for use with a gas engine driven pressure washer. FWIW I put an unloader and shutoff gun on one bay as an experiment to see if customers would be confused without the usual weep gun. No one ever seemed bothered by it.

 

[2Biz]

The check valves are there because they're unloaders. They're meant to be used with full shutoff guns, and when the trigger is released the pressure is trapped in the hose and the regulator "unloads" the pressure from the pump so it runs with no load on the motor. They're mainly meant for use with a gas engine driven pressure washer. FWIW I put an unloader and shutoff gun on one bay as an experiment to see if customers would be confused without the usual weep gun. No one ever seemed bothered by it.

OK, I'll bite again! You ever seen an engineer use a component in an invention that was totally designed for a different purpose? These unloaders are no different. Just becasue they were designed for a specific purpose, DOES NOT mean they can't be used in a different way to get the results you are looking for. In my case, and thousands of other Mark VII installations, they used the giant regulator/unloader that has a built in C/V that could also be used to keep weep from backfeeding through the pump and back to the gravity tank. When its plumbed with a weep gun, the unloader reacts just like a regulator. It doesn't unload and keeps constant pressure on the pump. I've had some of these regulators in service for up to 11 years now without having to touch them.

So basically I don't understand what your comment has to do with whether or not you need a CV to keep weep from backfeeding to the gravity tank...Maybe Mark VII had it figured out after all?!

 

[MEP001]

I never said it doesn't work, I was commenting on its intended purpose. I plumb my soap and wax solenoids backwards from their intended purpose because it eliminates the need for a check valve.

 

[1carwash1]

I never said it doesn't work, I was commenting on its intended purpose. I plumb my soap and wax solenoids backwards from their intended purpose because it eliminates the need for a check valve.

Is this because you are applying pressure in the same direction as the solenoid plunger spring and not against it?

 

[MEP001]

Is this because you are applying pressure in the same direction as the solenoid plunger spring and not against it?

Reversing the solenoid flow uses the solenoid spring pressure to stop the flow instead of using the pressure to keep it closed when off.

 

[1carwash1]

Reversing the solenoid flow uses the solenoid spring pressure to stop the flow instead of using the pressure to keep it closed when off.

that is exactly what I was trying to say. I would imagine this works for lower pressures but may prevent the plunger to open at some elevated pressure.

 

[MEP001]

that is exactly what I was trying to say. I would imagine this works for lower pressures but may prevent the plunger to open at some elevated pressure.

It's not stopping high pressure from the pump from backflowing, so it's not an issue. In my case, the solenoids can open with up to 150 PSI on the inlet side. You'd blow the pump seals if there's that much pressure on the reversed solenoids.

 

[2Biz]

To the original poster and others....IMHO and from a technical standpoint, a CV IS needed for two reasons....To keep weep from back feeding to the gravity tanks AND to keep wands from dripping water when not in use...The back feeding to the gravity tansk is pretty much common sense, but a dripping HP wand might leave you scratching your head?!

This past winter I shut down for a few days, pumping -20° washer fluid into all the HP hoses. I leave the hoses full of WF back to the pumps until I open back up. This time when opening back up (20° temps), one bay was froze solid up into the attic...First time I've had a bay freeze in years. What I noticed after that was this particular bay ALWAYS had wet floors over to the drain. Then noticed this bay was continually dripping, once about every 5 seconds, unlike the other bays...This is why the bay froze, it syphoned all the WF out of the hose and filled it with water during the time I shut down....I have Ball valves on my gravity tanks, from now on when I shut down, I'll also turn off the feeds from the gravity tanks to keep this from happening.

Finally this morning I had a chance to take the affected Giant Unloader/Regulator apart to check the built in CV. The Oring was worn pretty good, been in service for 11+ years...A new oring fixed the dripping problem.

So the CV stops the wands from dripping and also from backfeeding the gravity tanks...I can only see a lot of problems if you don't have one installed, either inline or inside the Giant unloader/regulator like Mark VII built into their systems. That is, unless you have "Perfect Sealing Seals and Seats" in your pumps, we all know this isn't possible long term.

The theory behind dripping wands is liquid has .433 LBS of pressure for every foot of head...The top of the water in my gravity tanks is about 24" above the tip of the wand as holstered in the bay. So water will seak lowest point, unrestricted. Even thought the CV is designed to keep water from backflowing to and through the pump, it also serves as a seal from water flowing in the opposite direction, as long as there is enough spring tension to hold the seat. In my case, just a little less than 1 psi....

 

[MEP001]

To the original poster and others....IMHO and from a technical standpoint, a CV IS needed for two reasons....To keep weep from back feeding to the gravity tanks AND to keep wands from dripping water when not in use...The back feeding to the gravity tansk is pretty much common sense, but a dripping HP wand might leave you scratching your head?!

I don't agree, but nearly all the car washes around here don't have the top of the tank higher than about 12" above the top of the pump. The only time I see constant dripping from the wand (I'm talking bad enough that in 20 years it'll wear a channel in the concrete) is when the spot free is pumped through the bay pump and the pressure reducing solenoid is a DEMA 453. They need 5 PSI to seat, and with the RO tank water as much as 8' above the pump it pushes its way through.

I agree that the backfeeding is going to always be an issue. I just don't like adding things to solve an issue that can be fixed without adding more parts to fail. I used to work with an old guy who handled our new equipment builds and turnkey construction. He got a bad batch of check valves for above the booms, and not only did he put one on every line (Four instead of the usual two we used), when they started causing problems his solution was to add MORE at the bottom of each solenoid stack in the room. By the time I found out the owner, a super nice lady who I'd known for years, was having all the problems, she was literally in tears over all the complaints and phone calls every day because things kept failing to work. Even the foam brush would lock up if it dipped below freezing at night. I went through and undid all his "work" and it's been running almost perfectly for the last 23 years. IIRC the last time there was an issue from a check valve, it was at the spot free tank and stuck closed, so I removed it.

 

[Dan kamsickas]

We've been building equipment for 40+ years without check valves on the soap and wax. We had Giant approach us a few years back to try their unloaders and gave us a really good price. Brought in a couple of cases. Put about a dozen in the field and every one failed. Switched back to SMC and no more issues. All the unused giant unloaders went in the scrap bin.