Keeping constant water pressure available for use

[SamRay73]

Hi,
I have some mini-greenhouse structures in which the humidity is controlled by atomizing misters. The misters operate by positive air and positive water pressure. Air and water solenoids open and close as needed to maintain a set point. Our air is supplied by an air compressor, which works just fine at maintaining a constant 50 psi or so. Our water supply, however, comes from a well that is shared by other facilities. So, depending on the demand at the time, our water supply pressure will vary between 25 and 75 psi. I would like to maintain 50 psi. I know I could install a holding tank and use a pump with a regulator, but I was hoping for something simpler. Can I use a booster pump continuously, and have it recirculate exess water back into the inlet? If not, what ideas would you have?
Thanks!
Sam

 

[hydtools]

Sounds like your water suppply does not have the flow capacity to supply all demands simultaneously, hence the pressure drop as other demands come on line. I would expect a booster pump would pull water from the other users and starve them. Sounds like a holding tank may be your answer to supply you when other users are on line.

Ted

 

[BigInch]

The only simplier thing I know is a high tank, pump up intermittantly on a high/low level control and feed your system continuously with a 50 psi pump running at your exact flowrate required.

Or size a booster pump for max required flowrate and recirculate excess back to inlet. May cause overheating when recirculating high flowrates, if the suction line is small, in which case you should recirculate back to a tank, or shut the pump off.

If you use a tank, you wouldn't have to regulate the pump discharge based on the widely varying suction pressure you have now. You could probably then select a pump to give you the exact head needed by the misters and you might not need a discharge regulator. With the suction pressure varying as it is now, a discharge pressure regulator is more than likely required to keep your flowrate reasonably within margin.

The tank will probably be the most economic solution over the long run.

From "BigInch's Extremely simple theory of everything."

 

[cvg]

a hydro-pneumatic system might be what you want:

http://www.peerlessxnet.com/documents/tibs/TIB-101_Hydro-Pneumatic-Pressure-Systems.pdf

 

[BigInch]

Isn't that more complicated?

From "BigInch's Extremely simple theory of everything."

 

[cvg]

depending on the capacity, these can be off the shelf units and simple. they make the smaller ones for home use on private water wells.

 

[SamRay73]

Thanks for the inputs! My flowrates will be very small since we're only talking about up to 16 misters. I just need the higher pressure. So, I'm not too worried about starving the other facilities. I've got a 1/2 hp booster available, so I'll try to employ that, and circulate the excess back to the inlet. I'll try to do a follow up post to let folks know how it works out.
Sam

 

[bimr]

You will need some type of control system.

If you want to maintain a constant pressure you will need a variable speed pump.

This is the same scenario that most high rise building designers must consider when designing the water plumbing. How to control the water pressure in multiple floor levels. Installation of booster pump sets consisting of variable speed pumps that draw water directly from the public water main is usually required.

http://www.pmengineer.com/CDA/Articles/Feature_Article/BNP_GUID_9-5-2006_A_10000000000000133285

Note that if you are drawing water from a public source, you need permission to repump.

Look for a pump manufacturer that makes a combination variable speed controller and pump.

http://completewatersystems.com/wp-content/uploads/2011/04/BRHYDROVAR.pdf

http://www.pumpshop.com/variablespeed/aquavar.html

 

[Artisi]

Have a look at Grundfos (model CH or JP) with a pressure tank, you should be able to set the pressure switch cut-in / cut-out settings to maintain a fairly constant system pressure.

It is a capital mistake to theorise before one has data. Insensibly one begins to twist facts to suit theories, instead of theories to suit facts. (Sherlock Holmes - A Scandal in Bohemia.)

 

[chicopee]

You'll need a reservoir as pointed out by the above responders or install a bigger pipe inside of the well so that at 25 psig you will still have the required flow.

 

[Compositepro]

You likely need to maintain a certain minimum pressure rather than constant pressure. A very small booster pump can add 20 or 30 psi to your supply pressure.

If supply pressure only drops for short periods, a small pressure tank with a check valve can be charged when your supply pressure is high and maintain pressure during the drops. Misters use little water.

 

[SamRay73]

OK, I chickened out of the booster pump idea. I invested in a tubine pump and a tank and installed a self-contained float valve. The turbine pump seemed ideal for low volume, high pressure. The tank refills as needed from the facility's well. The turbine pump draws from the tank and through a filter, and the discharge is divided into two paths: one to the misters and the other to a tank return. I installed a pressure gauge and a gate valve on the tank return to monitor/control the pressure. The pressure varies between 50 to 65 psi depending on the # of misters spraying at any given time, but that range is fine for my application, so overall the system is working well. I still need to install some sort of failsafe if the water level gets too low. I'd like to be able to install a probe in the water that can detect the water level, whether it be based on pressure of some sort of float based on the the actual level. Any recommendations for something fairly simple?
Thanks again,
Sam

 

[bimr]

There are a multiple options for level switches depending on the configuration of your tank:

http://www.tanksforless.com/Level-Control-Switches_c160.htm

http://www.liquidlevel.com/products_gallery2.asp

Gems:

http://www.gemssensors.com/Contact-...e/Multi-Point-Float-Level-Typical-Application

Grainger:

http://www.grainger.com/Grainger/float-switches/pump-controls/pumps/ecatalog/N-cc8