What are the merits of gravity feed hot water?

[OurTown]

Our wash was built with a 400K btu boiler connected to a 80 gallon storage tank (like an electric water heater without the heater elements in it) and a circulating pump. Then it is connected to a open (non pressurized) stainless tank with a float valve to keep it full. Out of the bottom of the tank it is gravity fed to each Cat 623 pump. There is a cold city water pressure solenoid valve just before it enters the pump to cool it down a little. It seems like an elaborate and inefficient setup. We are thinking of ways to make some room in our ER for some new equipment and would like to go with tankless water heaters. I think my real questions are:
1. Why is our water over heated and then cooled down before entering the pump?
2. Why is it built with gravity feed on the hot water instead of pressure?

 

[MEP001]

Are you sure that the solenoid is there to cool the water? Typically the solenoid is there to provide cold only when Rinse is selected. I'm not saying yours isn't how you said, but it would be unusual.

It's built on gravity feed so it can draw soap and water at the same time. If it were fed with pressure, you'd have to inject the soap. There are ways to do that which don't involve a downstream injector that will cost you 20% of your pressure.

There are no merits to it, that's just how it's been done for 50-odd years in this industry.

 

[OurTown]

Are you sure that the solenoid is there to cool the water? Typically the solenoid is there to provide cold only when Rinse is selected. I'm not saying yours isn't how you said, but it would be unusual.

It has a 3/4" ID hose from the gravity tank and I didn't see a solenoid valve on that. The pressure cold water goes to the solenoid valve through 3/8" OD polytubing. I'm not sure but it might be turned on only with rinse but it would still be warm going into the pump right?

 

[Main Street Carwash]

Typically there is a check valve on the line from the hot water tank to keep the city water pressure from backflowing into the tank thus feeding the pump only cold city water

 

[Randy]

We got rid of the gravity tank setup 25 years ago and went to a pressure fed system. We use a Generant HC regulator https://www.kleen-ritecorp.com/p-32...2-pressure-regulator-hc-series-5-125-psi.aspx and DEMA 203C injector https://www.kleen-ritecorp.com/p-1630-dema-203c-brass-38-in-c-series-injector-ryton-screw.aspx We very seldom have any problems with the Generant regulator and never have had a problem with the DEMA injector. By keeping a low positive pressure on the pump the pumps will last later, I can’t remember when I last had a pump problem.

 

[Main Street Carwash]

Randy, what pressure do you feed the pumps? Pressure fed pumps would definitely do better.

 

[MEP001]

It has a 3/4" ID hose from the gravity tank and I didn't see a solenoid valve on that. The pressure cold water goes to the solenoid valve through 3/8" OD polytubing. I'm not sure but it might be turned on only with rinse but it would still be warm going into the pump right?

Sounds like the typical D/H pump stands from late 70's or early 80's. On those it's definitely only going to open the solenoid when Rinse is selected. The idea is that when the solenoid is open there's enough flow to the pump (Yes, even through the 3/8" OD tubing) to close the check valve and stop the flow of hot water from the tank.

 

[2Biz]

We are thinking of ways to make some room in our ER for some new equipment and would like to go with tankless water heaters.

You might want to reconsider this unless you want to keep your big holding tank and circulators....There is plenty of threads on here that point out the restrictive nature of most demand heaters.

I got rid of the huge 350k btu boiler setup for hot water years ago. Did the research and settled on a High Efficiency NG Modulating/Condensing 55 gallon HTP Phoenix water heater with 1" inlets/outlets...You can set temp as low as 100° and it produces appr. 400 gallons of heated water an hour...(199kbtu rating)...I've never run out of hot water and even if it did, it won't starve your pumps like a demand heater can when plumbed direct to a smaller holding tank. Something to consider.

 

[Rudy]

Our town....sounds like an old Super Wash setup.....

 

[OurTown]

I looked into it further and it does have a check valve on it and it is just cold water on rinse. It is a Super Wash setup but it's not that old. (2003) To make it really simple for now we might just replace the boiler and storage tank with two tankless water heaters and keep the pumps gravity fed. At least we would save the room where they were. While we are on the subject of tankless water heaters which type? Condensing or non-condensing?

 

[2Biz]

Condensing for efficiency....Do you know what size gravity feed tank you'll be going with?

I have a Takagi 199k btu condensing/modulating demand that heats my floors. Its pretty awesome and has been flawless since I put it in over 4-5 years ago...

 

[OurTown]

Non-condensing for reliability? We would use the tank we have and the float is set to hold about 10 gallons.

 

[2Biz]

At 40 psi and 105 deg setting on my Takagi for floor heat, it puts out about 6.5 gpm. In order to get the 10 gpm rated output, you have to have 100 psi water pressure supplying it. I don't know how many bays or auto's you have, but even with 2 tankless heaters supplying water to a 10 gallon tank, I'd be leary...once you settle on a heater, d/l the manual and look at the flow chart. That will tell you the capacity output at your inlet psi pressure. Do the homework and math so there won't be any regrets.

 

[OurTown]

I'll take a closer look at the flow charts. They will be for only three SS bays.

 

[GoBuckeyes]

We got rid of the gravity tank setup 25 years ago and went to a pressure fed system. We use a Generant HC regulator https://www.kleen-ritecorp.com/p-32...2-pressure-regulator-hc-series-5-125-psi.aspx and DEMA 203C injector https://www.kleen-ritecorp.com/p-1630-dema-203c-brass-38-in-c-series-injector-ryton-screw.aspx We very seldom have any problems with the Generant regulator and never have had a problem with the DEMA injector. By keeping a low positive pressure on the pump the pumps will last later, I can’t remember when I last had a pump problem.

That is so funny....I currently have 4 washes with pressure fed pumps and one wash with gravity feed. I have always found the gravity feed to have far less headaches as there is so much less that can go wrong. No pressure regulators to adjust. No water inlet valves to maintain etc. I just saw there is another thread talking about inconsistent soap flow between bays...I’ll bet he has a psi fed system. On my list of projects and improvements is converting the pressure fed systems to gravity. Just goes to show...the grass is always greener.

 

[Randy]

That is so funny....I currently have 4 washes with pressure fed pumps and one wash with gravity feed. I have always found the gravity feed to have far less headaches as there is so much less that can go wrong. No pressure regulators to adjust. No water inlet valves to maintain etc. I just saw there is another thread talking about inconsistent soap flow between bays...I’ll bet he has a psi fed system. On my list of projects and improvements is converting the pressure fed systems to gravity. Just goes to show...the grass is always greener.

I must be living right. I very seldom ever have to touch anything on my pump stands. What kind of regulators and injectors are you using?

 

[GoBuckeyes]

We use Dole dual inlet water valves which have the identical diaphragms that hydrominders use. I’m not sure who makes the injector we use. They are much larger than the DEMA’s but cause little trouble. We also use the 1/2” Generant hot/cold regulator.

 

[MEP001]

We use Dole dual inlet water valves which have the identical diaphragms that hydrominders use. I’m not sure who makes the injector we use. They are much larger than the DEMA’s but cause little trouble. We also use the 1/2” Generant hot/cold regulator.

I tried the PR-1000A zero pressure regulators - they worked great, but the insert is chrome-plated brass and erodes, then the o-rings keep coming off and it no longer regulates pressure. If they'd make them from stainless it would be the way to go IMO.

I've thought about using Dema Mix-Rite or Dosatron pumps for chemicals to the pumps and just running everything at city pressure, I just haven't felt like buying them to see if it would work.

 

[washnvac]

I have the same system made in 2004 at a location I bought. It is way over engineered. I guess Coleman liked selling all that equipment. You would never use all that hot water. I eliminated the 80 gallon storage, and re-plumbed the circulator to go back directly to the open tank. I then installed a multiplexer to break the t-stat wire when not in use. Moved the t-stat to the open tank. The multiplexer is activated by the 24 volt hot in any bay. This closes the signal loop to the t-sat, and brings the boiler on if the open tank is not at 115. So at any time I am only keeping the 15 gallons or so hot in the open tank. When no bays are used, the boiler never comes on.

This is a cheap way to lower your gas bill, and sort of create an on-demand heater with your existing boiler.

 

[GoBuckeyes]

I tried the PR-1000A zero pressure regulators - they worked great, but the insert is chrome-plated brass and erodes, then the o-rings keep coming off and it no longer regulates pressure. If they'd make them from stainless it would be the way to go IMO.

I've thought about using Dema Mix-Rite or Dosatron pumps for chemicals to the pumps and just running everything at city pressure, I just haven't felt like buying them to see if it would work.

MEP, I have a brand new zero pressure regulator sitting on my shelf that I bought to try out a few years ago. Shortly after buying it I started reading a thread that talked about all the problems people had with them and the specific way they needed to be plumbed for when the pump goes into by-pass. Needles to say, I never installed it.

The Mix-Rite and Dosatrons are interesting alternatives and seem like they should work but again, thats a $1000 science project I don't have time for. To me the gravity feed is still simpler and bulletproof. With the chemical pump set up you still have one or two water inlet solenoids per bay. It also adds two more mutliplexors, one for soap and one for wax, into the mix. If you don't have solenoid for each chemical pump you run the risk of pumping away a bucket of soap or wax if one of the bay solenoids doesn't close.