Maintaining Water Pressure - Car Wash

[loewem]

Hello, I've been reading through the posts on this forum this evening in hopes of learning what I need to do to maintain the water pressure at my car wash.  Full disclosure...I have little idea what I am talking about, so I apologize if I don't explain this well. 

My wash has five self-service bays and one in-bay automatic (IBA) wash.  I have a 2 inch main pipe coming into the wash, but I understand that the water meter that feeds my wash might be smaller.  I'm going to speak with this town this week to determine the size of the meter. The static water pressure is 70 PSI and the dymanic pressure is 65 PSI.  The self-service bays require 3.5 gallons per minute when the high pressure is in use (17.5 gpm if all are in use at the same time).  The self-service bays are gravity fed via 60 gallon rinse tank which is supplied by a 1 inch watts float valve.  I've not been able to determine the gpm requirement of the IBA and I'm waiting on the manufacturer to respond to an e-mail or call me with some information.  I think that maximum demand for the IBA is about 28 gpm.  I also have a reverse osmosis system that kicks on a frequent basis.  I have not tried calculating the gpm demand of that system, but I think I can figure it out.

I have an opportunity to add a second IBA which will have a similar demand to the current IBA and I'm concerned about water supply and pressure.  In attempt to free up space in my equipment room I installed a dema mixrite chemical proportioner for a wax that I provide in my self-service bays.  The mixrite is compact and works much better than my previous set up that relied on an air powered diaphragm pump to push the wax.  I've been trying to tweak the mixrite and have noticed that it stops working altogether when the float valve for the IBA opens up.  Performance drops off noticeably when the Reverse Osmosis system kicks on. 

I'm hoping that I can have a system installed to maintain the dynamic water pressure at 65 PSI.  Any thoughts or information to point me in the right direction for calculating the needs at my wash and possible options that exist would be greatly appreciated.  I've looked at a lot of different booster pumps/booster systems online, but I'm kind of lost. 

Thanks

[Cary Austin]

We do lots of car washes with CSV's.  With a CSV controlling the right booster pump, we can maintain a constant 65 or whatever pressure you require as flow rates vary from a little to a lot.  However, you can't boost or pump water unless it is available.  So if you try to draw more water through the meter than the meter can supply, you will still be low on water and pressure.  If the city can supply a larger meter and deliver as much water as you need for peak demands, you can just boost city pressure up and maintain the 65 constant that you need.  Many times car washes will have to put in a 2000-3000 gallon storage tank to be fed by the small city meter, then the booster pump system can draw as much as needed from the storage tank for peak demands.  The storage tank gives a buffer between the small volume of water the city meter can supply and the larger peak demands of the car wash when multiple systems are operating at the same time.

[loewem]

Thanks for the response.  I found out that there is a two inch water meter/main that supplies my car wash.  How can I go about determining if the water supply is adequate, so that I can work to boost the pressure?  What type of business deals with type of issue?  I've talked to two plumbers and I'm thinking that I need to find someone who specializes in these issues, but not sure what to look for.  I like the idea of a large supply tank.  I've got a tank to capture the reject water from my reverse osmosis system and I pump that water into my rinse tank via a float valve and submersible pump.  I've got the float for the city water shutting off when the rinse tank is about 2/3 full and reject water fills to the top before shutting off.  I've been thinking about adding a feed from the city water to the reject tank and using a mix of reject water and city water to gravity feed my IBA rinse tanks.  The tank is 400 gallons and I think that it would easily keep up with demand and eliminate the need to use the 1 inch float valve.  I'm planning to have a larger rinse tank to feed my self service pumps, so that I won't need a 1 inch float valve on that side.  I've also had the thought of capturing rain water to use for all rinse functions (self service and IBA). Thinking that I could do a combination captured rain water and city water with that type of set up.  Water is by far my biggest expense, so reducing that expense by any amount would be helpful to my bottom line.  The city charges me 1:1 for sewage costs, so the savings would be multiplied if I could capture some rain water for rinsing.  Do you have any thoughts on this idea?  Am I dreaming?  I appreciate your help.

[Cary Austin]

My first thought is to drill a well.  Not only will the water quality probably be better than city water, but you can pump for pennies what cost thousands of dollars to purchase from someone else.  Even a small well can produce a lot of water for a car wash if you have enough storage.  I work with car washes that have a good producing well, and using a Cycle Stop Valve pump directly to all the demands of the car wash. I also work with others who only have a small well available to them.  They pump the 4 GPM well into a storage tank 1440 minutes of everyday, and can store up to 5,700 gallons to use everyday at the car wash.  Even others supply what they can from their well, and supplement with city water when needed.  There really is no limit to how many ways you can skin this cat.

But I also work with those who do not have well water available, or the city does not allow drilling (wonder why? $$$).  Even in these cases sometimes a storage tank is either required by the city or demanded by the size of the meter.  Many times the city will not allow a booster pump to be directly connected to a city meter.  They would require you to fill a storage or cistern type tank using a float valve from the city line.  Then the booster pump would draw from the storage tank and supply the car wash.

With storage, you would not be "sucking" on the city line directly, which can cause problems if/when the city water is off or is in limited supply.  With a storage tank type system, the city meter only needs to supply the amount being used, less the amount available from the storage tank.  So the larger the storage tank, the slower the city water can feed it and vice versa. 

Then either way you need a booster pump to draw from the storage tank and supply the car wash.  The booster pump needs to be large enough to supply the pressure required with all the demands that can be on running at the same time.  Then a Cycle Stop Valve will make that pump produce smaller, even tiny amounts of water that maybe used during off peak times.  Working with a small pressure tank and pressure switch, the Cycle Stop Valve system will also shut the pump off when no water is required, and turn it on automatically when water is needed anywhere.

[Cary Austin]

Here is a cad drawing of a similar system.  I will see if I can find a picture.

[Cary Austin]

Something like this.