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Old 05-12-2009, 11:19 PM   #1
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Default check valve back pressure

So I have a DO WI kit installed and working. I was working on a failsafe setup to limit the boost unless I know I have water pressure on the high side of the pump. I have a DO 6-30 psi adjustable pressure switch mounted on a tee right at the outlet of the pump. The switch is set for 30 psi. According to the DO web site the check valve opens at 16 psi.

Here is the deal... When I activate the pump, then deactivate it, the switch stays on according to the DMM I have on the switch. This is all with the engine off of course. One would think the check valve would continue to flow until the differential pressure is 16 psi. Since the switch is set at 30, it should turn off again when the pump stops running.

So I wanted to keep the failsafe switch at the pump for convenience. But, I might have to move things around and put the switch between the check valve and the nozzle for this to work correctly. Basically I need the switch to shut off immediately as soon as there is no longer adequate pressure from the pump.

Thoughts?
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Old 05-12-2009, 11:29 PM   #2
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Quote:
Originally Posted by ZX-Tex View Post

Here is the deal... When I activate the pump, then deactivate it, the switch stays on according to the DMM I have on the switch. This is all with the engine off of course. One would think the check valve would continue to flow until the differential pressure is 16 psi. Since the switch is set at 30, it should turn off again when the pump stops running.

So I wanted to keep the failsafe switch at the pump for convenience. But, I might have to move things around and put the switch between the check valve and the nozzle for this to work correctly. Basically I need the switch to shut off immediately as soon as there is no longer adequate pressure from the pump.

Thoughts?
This is somewhat incorrect. I just began working my Mechanical Engineering Summer internship at a valve company based out of connecticut (Lee co). I work with the Check and Pressure relief valve group and have been running a lot of flow testing so far.

16 PSID (differential pressure) is your cracking pressure. This is the minimum pressure your valve will start flowing on the up run( pressure increasing). 30 psid is the max working pressure. Your cracking pressure is not the same as the point at which it closes on the down run (depending on specs). For example today I worked on a certian valve (proprietary info blah blah blah) that had a cracking pressure of 4700 PSID and a working pressure of 5400 PSID but its closing pressure was 4300 PSID.


TO HELP YOU:
have you thought of a halls type switch or a pressure transducer to measure the pressure as a voltage?
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Old 05-13-2009, 11:48 PM   #3
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Well, I have an even simpler explanation. It turns out the nozzle was clogged
It is working as expected now. Thanks for the info just the same.
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Old 05-14-2009, 12:00 AM   #4
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haha, the simplest thing is usually the issue. I just wanted to sound smart
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