Pressure gauge indicates zero during normal operation???

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KCD

KCD

Well-known member
Apr 9, 2021
65
Clinton, MD
Pressure gauge on the filtration unit of my pool indicates zero during normal operation when the valves are open to the drain, skimmers and the return. The gauge is not broken. There appear to be no leaks; and the flow seems normal through the skimmers and the return lines. When one of the return lines is closed, the pressure gauge shows 6 psi. What could cause the gauge to show zero pressure under these conditions???
 
duraleigh said:
I would think that cartridge filter and the 1.5HP single speed pump would produce about 10-12 psi with everything open. How do you know your gauge is not faulty?
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The gauge was being replaced because the old one was also showing zero. It's not likely that there would be two gauges with the same problem at the same time on a system.
 
JamesW said:
Can you show the system?

What is the system elevation relative to the pool?

Is the filter plumbed correctly with the In and Out?
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The system is a few feet above the pool. The system appears to be situated correctly. How would I determine if it is out of plumb and how would it cause zero pressure?
 

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Are you sure that the pump is a Jandy FHPM1.5 single speed 1.5 HP pump?

That’s not a DOE compliant pump, which I would find unacceptable.

The head loss from the filter is pretty low by design and the returns are splitting half of the water, which creates low head loss.

If the gauge is 8 feet above the water, it’s possible that the gauge could read zero, but I would expect a few psi.

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*Pumps not meeting DOE compliance standards will cease manufacturing on or before July 18, 2021.
 

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The pressure gauge is at the top of the filtration tank, about 5' above the surface of the pool. See pics below taken during construction and the name plate on the pump. If the gravity flow from the filtration tank to pool is equal to pump flow into the tank, the pressure gauge on the tank should read zero. That would explain why the pressure is zero in my setup. Now the question is, how do I know when to clean the filters? The manufacturer recommends cleaning the filters based on the increase in gauge pressure indication. I may have to partially close a return line valve, just enough to get a pressure reading, as a baseline for determining the pressure increase due to dirty filter.
 

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If we assume a flow rate of 80 GPM, that puts the filter head loss at about 10 feet.

The flow will dynamically balance between the 2" return and the 1.5" return and about 25 GPM will go to the 1.5" line and about 55 GPM will go to the 2" line for a head loss of about 4 feet.

That makes a total of 14 feet of head loss.

2 psi is about 4.62 feet of head.

14 - 4.62 = 9.38 feet.

So, if the gauge is more than 9.38 feet above the water, the gauge might not register.

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KCD said:
Now the question is, how do I know when to clean the filters?
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As the filters get dirty, the pressure will begin to rise.

A 0 to 30 psi gauge that starts at zero should register some pressure.

Based on your setup, I would expect some pressure.

Maybe there is an issue with the suction?
 
Based on your setup, I would expect about 4 psi, which is the first white line.

If we assume 2 feet of head loss for the returns and 10 for the filter, that's 12 total - 5 = 7 feet, which is 3 psi, which is halfway between the lowest reading and the first white line.
 
JamesW said:
Are you sure that the pump is a Jandy FHPM1.5 single speed 1.5 HP pump?

That’s not a DOE compliant pump, which I would find unacceptable.

The head loss from the filter is pretty low by design and the returns are splitting half of the water, which creates low head loss.

If the gauge is 8 feet above the water, it’s possible that the gauge could read zero, but I would expect a few psi.

*Pumps not meeting DOE compliance standards will cease manufacturing on or before July 18, 2021.
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Thanks for bringing that up. The pool is still under construction so I will bring it to attention of PB. I doubled checked and it is Jandy FHPM1.5. See pic.
 

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The pump was made before the cutoff, so it is still legal to sell, but I would not have a 1.5 HP single speed pump.

For a new install, I would require a variable speed pump.
 
KCD said:
Any ideas regarding finding issues with the suction?
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I would move the check valve from in front of the pump to after the pump between the pump and filter.

You can get a vacuum gauge to measure the vacuum pressure at the pump's front drain plug port.

Be careful not to overtighten the gauge or the plastic can crack.
 

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