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apbling

Unregistered

1

Thursday, July 4th 2013, 9:00am

pressure relief valve issues

Hi,

Hope I putting this in the correct area. I have a Rainbird controller, Orbit pump start relay, 1 1/4" sandpoint w/ check valve, 1 hp jet pump. I have a 1" header going about 5 feet over to my 5 Hunter valves that feed my zones. I'm having an issue trying to fit a pressure relief valve on the system. I had a pressure switch (used pump) but it was giving me issues. Local sprinkler guy said get rid of switch and use a pressure relief. ok, sounds good. Problem is my pump dead heads abou 60-65 psi. So I'd like to get one for 58-62 psi roughly. Problem is when controller tells the system to start the pump starts right away and there is a 2 second delay before the valve opens. During this 2 sec period the pump is running but dead headed and the pressure is just above 60. Then the valve opens and life goes on. How am I supposed to use a relief valve if there are momentary dead heads that would cause the relief to open? I'm an engineer and work with pumps and such at work all the time, but we would program the valve to open before the pump starts, avoiding this issue.

thanks.

Wet_Boots

Supreme Member

Posts: 4,054

Location: Metro NYC

2

Thursday, July 4th 2013, 11:12am

You simply don't have the 'headroom' to set a pressure relief valve at a point where it is useful to jet pumps.

That being said, you can deadhead a jet pump without killing it, because it is circulating water to the built-in ejector.

If you want jet pump protection for all occasions, you have to go thermal.

Apbling

Unregistered

3

Thursday, July 4th 2013, 1:09pm

Thanks wet boots. I know nothing about jet pumps, just centrifugal. I'm not sure if I'm using the jet pump in the traditional sense though. My buddy had it set up on a deep well and used a jack box or something. I had to buy a special part to screw in the side of the head to make it setup for shallow well. Does this setup still operate like you mentioned in your reply?

Wet_Boots

Supreme Member

Posts: 4,054

Location: Metro NYC

4

Thursday, July 4th 2013, 2:57pm

you are describing a bolt-on ejector assembly - all jet pumps have an ejector - so-called Shallow Well Jet Pumps have the ejector built into the pump - Convertible Jet Pumps use the separate ejector assembly

Apbling

Unregistered

5

Thursday, July 4th 2013, 7:55pm

Ok makes sense. Care to explain what you mean by "headroom"?

Wet_Boots

Supreme Member

Posts: 4,054

Location: Metro NYC

6

Thursday, July 4th 2013, 9:08pm

"headroom" means you can operate the device effectively - a jet pump running at 60 psi with a shutoff pressure of 65 psi gives you insufficient headroom for a relief valve, compared to a deep-well submersible pump with a shutoff pressure of 190 psi

a pressure relief valve opens gradually as pressure rises, instead of snapping open like a switch - not good protection for your jet pump

apbling

Unregistered

7

Friday, July 5th 2013, 8:35am

Ok, then what is the difference between my jet pump (it operates about 40-50 psi, just it has that 2 second 60+ psi period when it's dead headed) and a centrifugal pump? Either way the pump will be dead headed and running for a period of time before the zone valve opens.

Wet_Boots

Supreme Member

Posts: 4,054

Location: Metro NYC

8

Friday, July 5th 2013, 8:45am

I think you need to google some of these phrases and spend some quality time reading tutorial pages.

apbling

Unregistered

9

Saturday, July 6th 2013, 8:18am

I wasn't asking the difference between the pumps, I'm asking why you said I don't have the "head room" because I have a jet pump. Either way, if it's a jet pump or a centrifugal pump, it will be momentarily dead headed and will produce it's dead head pressure. Whether its 60 psi, 40 psi or 100 psi. I would like to get a PSV and set it for just under my dead head pressure so in the even that a valve fails the PSV will open and protect the pump. You say that a PSV is not a good idea for a jet pump. You mentioned that my shut off pressure is 65 and I operate at 60 - I don't, the pump operates normally in the 40-45 psi range, with the valve open.

What I'm really getting at is this: I see people recommend to others to have a PSV on their system. In a case like mine, where the pump is momentarily deaded head and produces deadhead pressure, how can you ever size a PSV that will open when your valve fails, but not everytime you start the system because the zone valves don't open fast enough.

And, I did read the tutorials. I googled stuff. Alot. I'm a chemical engineer and I work with pumps and piping systems everyday at work. This issue I am having is pissing me off to no end because I cannot figure it out. I wish I could just delay the pump relay from starting by 2 seconds and life would go on.

Wet_Boots

Supreme Member

Posts: 4,054

Location: Metro NYC

10

Saturday, July 6th 2013, 9:56am

If you read a good jet pump tutorial, you would already know a jet pump recirculates a portion of the water it pumps.

For the time and money spent messing around with the pump relay and pressure relief valve, you could already have a pressure switch and baby pressure tank controlling pump operation.

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