spot free rinse back flow

[usfbob]

Hello Everyone,

I have been checking out this site for a few years now and you all have been very helpful. Been in the car wash business for almost 6 years and have learned a lot with your help. I have a 6 bay ss wash and in 1 of the bays when the spot free rinse is in use i am getting a little back flow of water (about 40psi) into my pump. I have checked or replaced check valves in the attic out by the bay and nothing seems to fix the problem. I have checked and have not found any leaks at the pump and have eliminated the weep system (down in the Tampa Bay area of Florida, don't have to worry about freeze). Any ideas of other things I might check would be greatly appreciated.

Bob

 

[MEP001]

How can you tell there's backflow? Are you seeing something back-filling to a tank or are you seeing some pressure on the gauge? If it's the latter, there may be a check valve on the high-pressure line that's failed.

 

[PaulLovesJamie]

+1... I cant think of anything other than the check valve. Unless the "backflow" is in a bay other than the one using SFR, in which case it probably needs a solenoid cleanout/repair.

 

[usfbob]

Thanks for the replies. The back flow is in the same bay as the spot free. I noticed the problem because when the spot free was in use and I was in the equipment room I heard a buzzing sound which turned out to be the wax tubing shaking against the pump stand. I then checked the gauge and it was showing about 40 psi of back pressure. Currently there are no check valves on the high pressure hose running from the pump to the bay. I put one on the high pressure line in the attic at the bay and this did cure the problem but then another local car wash owner told me to never put a check valve on the high pressure line because it makes the pump work to hard. You guys on the message board have saved me many of times with out your knowledge so I trust what you say more than what he told me. So if you are talking about adding the check valve on the high pressure hose I will do it.

Thanks for the help

 

[MEP001]

The check valve on the high-pressure line is a stopgap cure - there's almost certainly a check valve somewhere else that has failed, either one specifically for the soap/wax lines or a common one for soap, wax and hot water supply. If there's a cold water supply to the rinse for each bay, you're still going to have backflow into your chemical tanks, so the real problem needs to be corrected.

Post some pictures of your equipment and the plumbing - I'd suggest signing up to a free image hosting site (I prefer imageshack.us).

 

[Jeff_L]

Personally I wouldn't put a check valve in the high pressure pathway, I don't have a technical reason why other than I don't like the idea of any obstructions in that line. I'm sure an engineer on this board can confirm/deny whether there should be one in the line or not.

You say you see 40psi on the gauge, I assume that's on the HP pump? Do you see any back-flow into a tank anywhere? Does your HP source gravity feed from a tank or is it fed directly from city pressure?

 

[MEP001]

Personally I wouldn't put a check valve in the high pressure pathway, I don't have a technical reason why other than I don't like the idea of any obstructions in that line. I'm sure an engineer on this board can confirm/deny whether there should be one in the line or not.

I don't know of any technical reason why you wouldn't put a check valve on the high-pressure line, but I can think of two good reasons not to: it's not necessary if everything else is working properly, and it's something else to potentially fail.

 

[usfbob]

Personally I wouldn't put a check valve in the high pressure pathway, I don't have a technical reason why other than I don't like the idea of any obstructions in that line. I'm sure an engineer on this board can confirm/deny whether there should be one in the line or not.

You say you see 40psi on the gauge, I assume that's on the HP pump? Do you see any back-flow into a tank anywhere? Does your HP source gravity feed from a tank or is it fed directly from city pressure?

I have not noticed back flow into a tank. The HP source is gravity fed from a tank which has what appears to be a rather large pvc check valve on each line. I will check that in the morning. That is the only check valve I see that has anything to do with the feed to the high pressure pumps. Thanks for your help and will check in the morning and see if that is the problem.

 

[MEP001]

I have not noticed back flow into a tank.

That's what is happening when you heard the wax line shaking. There may be another check valve on the soap and wax lines, or the solenoids were deliberately installed backwards to eliminate the need for a check valve and that valve was replaced and plumbed per its label.

 

[Jeff_L]

I don't know of any technical reason why you wouldn't put a check valve on the high-pressure line, but I can think of two good reasons not to: it's not necessary if everything else is working properly, and it's something else to potentially fail.

Wouldn't the valve be an obstruction in the line and decrease the velocity of flow by some measure? That's the reason why I was thinking you wouldn't want a check valve in the HP line. I figure the less obstructions, bends, etc the HP line has to go through before coming out the wand, the better.

 

[usfbob]

Thanks to everyone for the great suggestions. I went through and checked or replaced all check valves and solenoids and nothing had changed. So I started from the very beginning and started tracing all the lines and found a very very small leak on the soap line running from the solenoid to the pump. The leak was a drop every 5 or 10 seconds when in use and it was under the back of the pump that was on the bottom of the pump stand making it very hard to find. It must have been enough to create a vacuum and back flow because after I replaced the line the problem was solved. Thank you all so much for your help.

 

[MEP001]

I would keep an eye on things for a while, because I doubt you've fully solved your problem. You said you checked solenoids, but a properly installed solenoid provides almost no resistance to flow in the opposite direction. If you have cold water supplied to the pumps at city pressure, then there needs to be something on the soap/wax lines to prevent that from backflowing into those tanks. There's either a check valve (It can use the same check valve as the hot water supply if it tees in before it) or in some cases the soap/wax solenoids are deliberately plumbed backwards. If there is no city pressure for rinse and no check valve on the soap/wax supply of the pump, then the pump itself is what keeps spot-free from backing up into the tanks, which means you have a problem with the pump on that bay which needs to be corrected.

 

[usfbob]

Thanks for all you help. I check or replaced all the check valves and solenoids with no luck. I decided to start from the beginning and checked every line coming in and out of the pump and in the very back of the pump, which happens to be on the bottom of the stand with another pump above it, I found an extremely small leak (about 1 drop every 5 or 10 seconds) in the hp soap feed line. I replaced this line and the problem was resolved. I guess the small leak must have been creating a vacuum causing the back flow. Again I appreciate everyones help. Thanks again.

 

[usfbob]

I would keep an eye on things for a while, because I doubt you've fully solved your problem. You said you checked solenoids, but a properly installed solenoid provides almost no resistance to flow in the opposite direction. If you have cold water supplied to the pumps at city pressure, then there needs to be something on the soap/wax lines to prevent that from backflowing into those tanks. There's either a check valve (It can use the same check valve as the hot water supply if it tees in before it) or in some cases the soap/wax solenoids are deliberately plumbed backwards. If there is no city pressure for rinse and no check valve on the soap/wax supply of the pump, then the pump itself is what keeps spot-free from backing up into the tanks, which means you have a problem with the pump on that bay which needs to be corrected.

There is no city pressure for rinse and I am beginning to think you are right about a problem with the pump. I noticed today that when any low pressure function is being used the gauge on the pump is showing 40 psi of back pressure. I have shut the bay down for now as I am not able to get to work on the pump for a few days. Thanks again.

 

[usfbob]

My wax and high pressure soap are gravity fed from holding tanks. The wax has a simple shut off valve, so I did a test by turning that valve off to simulate having a check valve there, and then ran the spot free. What happened was my back pressure gauge went up to 120 psi. I am definitely thinking MEP001 is right and must be a pump problem.