Cavitation Issue

[washme1]

I think the problem started on very busy day yesterday when my spotfree wasn't keeping up with demand. Cavitation in all ss bays (4) except one that just had motor replaced. When SF tank refilled, problem persisted. Only occurs on hp wash and wax but hp rinse is fine. Motors are very warm. I shut one bay down for a couple of hours to cool motor. Problem persists. Then when I went back to carwash late in evening, all ss bays working properly. Today, another very busy day. Everything was fine until about 2PM and the 4 bays are cavitating again, but not the one with new motor. Spotfree tank with adequate water. Motors are pretty warm. Any ideas?

 

[DiamondWash]

Are your supply tanks full of chemicals "hp soap and wax" if those go empty you pull air into the system causing that noise.

 

[under pressure]

Im guessing you dont have a holding tank for your water, do you have a bladder tank? sounds like there is too much demand and not enough water,

 

[washme1]

Are your supply tanks full of chemicals "hp soap and wax" if those go empty you pull air into the system causing that noise.

Yes, supply tanks are full.

 

[washme1]

Im guessing you dont have a holding tank for your water, do you have a bladder tank? sounds like there is too much demand and not enough water,

I have a bladder tank but don't know much about it. It's about 5 gal, near the water meter. About five years old. About 20% of my chemical tank is a hot water reservoir.

 

[MEP001]

Cavitation is caused when your pumps can't draw enough water through the feed. This would be unlikely on a gravity-feed system - that would mean something is intermittently stopping flow from the tank to all the pumps. My first guess would be that you have a pump that needs to be rebuilt, and someone ran a function in that bay (Tire cleaner or presoak) that has air mixed in with it, and the air backed up through the high-pressure line, through the pump and back into the supply line for all the pumps.

Does your spot-free for the bays have its own separate pump or does it run through the high-pressure pumps? If it's the latter, that's where air would be getting into the high-pressure pumps and causing your problem.

 

[washme1]

Cavitation is caused when your pumps can't draw enough water through the feed. This would be unlikely on a gravity-feed system - that would mean something is intermittently stopping flow from the tank to all the pumps. My first guess would be that you have a pump that needs to be rebuilt, and someone ran a function in that bay (Tire cleaner or presoak) that has air mixed in with it, and the air backed up through the high-pressure line, through the pump and back into the supply line for all the pumps.

Does your spot-free for the bays have its own separate pump or does it run through the high-pressure pumps? If it's the latter, that's where air would be getting into the high-pressure pumps and causing your problem.

My spot-free has a separate pump. If a pump needs to be rebuilt, why would it operate properly on hp rinse? How would I determine which pump has the problem?

 

[PaulLovesJamie]

Cavitation is caused when your pumps can't draw enough water through the feed.

Or you're getting air into the line.

something is intermittently stopping flow from the tank to all the pumps.

Since its all bays at the same time, I also think you're getting reduced flow to the pumps.

Perhaps a clogged check valve? Corroded fitting restricting flow?

I suspect your bladder tank may be undersized or in need of replacement.

Do you have a separate feed to the pumps for cold water rinse?

I doubt it's related to the motors, and since it's all bays at the same time I doubt it's related to a pump needing to be rebuilt.

 

[ted mcmeekin]

Your bladder tank may be water solid--does sf pump run often for short periods. If so drain bladder tank (be sure you vent it), check air pressure in bladder--tag on top of tank will give proper pressure. May be too low,water solid or ruptured bladder. We have to do this periodically as our bladders slowly lose pressure--may be slow leak in air valve.

Ted

 

[MEP001]

Cavitation is caused when your pumps can't draw enough water through the feed.

Or you're getting air into the line.

That's not cavitation. It has the same result (Noise and loss of pressure), but cavitation is specifically the creation of vapor in a liquid caused by a negative pressure of the fluid being pumped, which in this case would be from a restriction to its inlet.

Since its all bays at the same time, I also think you're getting reduced flow to the pumps.

I think that's much less likely than air getting through as I described. It's not typical for a self-serve bench to have a common check valve between all the pumps and the tank, so there should be nothing common to all pumps to cause cavitation.

I suspect your bladder tank may be undersized or in need of replacement.

Since the holding tanks are staying full, this bladder tank is either on the water heater or the incoming water main and is not part of the problem.

 

[MEP001]

If a pump needs to be rebuilt, why would it operate properly on hp rinse?

If a pair of check valves in the pump, a high-pressure seal or the regulator aren't seating 100% in addition to a bad check valve on the hot water line, it can let some flow back through but not be bad enough to affect the pressure. I've seen this happen many times.

How would I determine which pump has the problem?

Does the spot-free tee in at the boom along with the high-pressure and the tire cleaner/presoak? If so, the fastest way to find it is to run the bay on tire cleaner for a minute, run spot-free until it's clear, then run high-pressure. If you get a significant blast of tire cleaner, that is what has backed up into the high-pressure line.

 

[washme1]

Thank you for all of the advice. When my distributor closed all of the weep valves, the problem stopped. Here's what the problem was. The lines for my weep are plumbed into the inlet sides of the pumps. Have been that way since the car wash was built in '87. He says I need to plumb them to the outlet side. I will do that this morning as we were super busy yesterday.

 

[MEP001]

That means it was air from something backing up through one pump, through the weep and into the water lines for all the bays.

 

[washme1]

That means it was air from something backing up through one pump, through the weep and into the water lines for all the bays.

Is there something else I need to do to prevent further issues?

 

[MEP001]

As I said before, there's a pump that needs servicing which was the initial cause of the problem, but it may not be bad enough to detect yet by pulsating or loss of pressure. The weep on the inlet of the pump is probably after the check valve to the tanks, so when air gets through it can flow freely to all the pumps through the weep. Moving the weep to the outlet will solve the problem.

 

[washme1]

As I said before, there's a pump that needs servicing which was the initial cause of the problem, but it may not be bad enough to detect yet by pulsating or loss of pressure. The weep on the inlet of the pump is probably after the check valve to the tanks, so when air gets through it can flow freely to all the pumps through the weep. Moving the weep to the outlet will solve the problem.

Thanks MEP. I never really understood before how the air gets back to the other pumps.

 

[Randy]

You should never plumb in the weep system on the inlet side of the pump, you’re asking for problems down the road. When you move the weep lines over to the discharge side of the pump use a high quality Stainless steel check valve this will prevent a lot of problems. We’ve been using a ¼” Ball valve on our weep systems now, we give up on the Needle valves they didn’t seem to last too long.

 

[washme1]

You should never plumb in the weep system on the inlet side of the pump, you’re asking for problems down the road. When you move the weep lines over to the discharge side of the pump use a high quality Stainless steel check valve this will prevent a lot of problems. We’ve been using a ¼” Ball valve on our weep systems now, we give up on the Needle valves they didn’t seem to last too long.

Thanks Randy. I'll replace my brass check valves with stainless.