how to find blockage in recirculation loop

[semenzato]

Greetings,

I am experiencing intermittent blockage of the PVC pipes between
the filter and the pool. The pressure gauge at the filter shows higher
than normal pressure, and there is very little flow. If I turn off
and on the pump several times, the blockage goes away.

The question is, how do I find where it is? I have examined
the filter and nothing seems wrong with it. After the filter
there is a check valve (one-way valve) and I strongly suspect
that's the culprit. Then there is a three-way valve to optionally
direct the flow through the solar panels. Then there is a manual
valve, and then the Pool Pilot chlorine generator.

Pressure gauges on the web are cheap ($5 to $10).
I don't mind buying two or three and leaving them
permanently installed in order to isolate this one problem.
But they have copper male threads and I don't know
if there is any simple way of installing them on 1.5"
PVC pipes. Any suggestions?

Thanks!
Luigi Semenzato

[duraleigh]

If your pressure guage reads higher during the blockage, the problem is somewhere between the pressure side of the pump and the return eyeballs.

[cleancloths]

I would be willing to bet the check valve is the culprit. It is quite hard to get a blockage in PVC pipe - what do you suspect this blockage might be?

[mas985]

During one of the high pressure moments, leave the pump on and tap lightly with a hammer on the check valve and see if it lets loose. If it is stuck it should swing open and the pressure drop.

[semenzato]

Thank you for the advice. I just tried tapping the valve but it didn't have any
effect. I still suspect the valve, though.

I tapped reasonably hard but I had to make an educated guess as to how hard
to avoid cracking the valve casing.

Oh well, I guess I'll replace the valve and pray that's the problem.
I will post on this thread as soon as I do it.

Thanks!
Luigi

30'x16' (irregular) indoor gunite/plaster pool, about 10k gal
Pool Pilot SWCG, 3/4 HP recirc pump, solar panels, heat
exchanger from 200 BTU/hour Viesmann boiler

[Poconos]

Whacking PVC with a piece of 2x4, not pressure treated, is pretty safe. Pressure treated seems a little harder, but still softer than a hammer. Or, use a piece of PVC pipe.
Al

[semenzato]

Whacking PVC with a piece of 2x4, not pressure treated, is pretty safe. Pressure treated seems a little harder, but still softer than a hammer. Or, use a piece of PVC pipe.
Al

Thanks, I appreciate the PVC-whacking advice.
I am quickly becoming an expert on whacking PVC.

I found drawings on the Web on how this particular check valve
is built. There is just a little door. I am guessing that the door
doesn't stick completely closed, because there is a tiny bit of flow,
which varies from run to run. So it may be the hinge. In this
case it's not clear that further whacking will reveal anything,
because the door may be required to jiggle a bit to become loose
(instead of just unsticking from the opening) and the whacking
is not necessarily going to be effective.

I found a place that sells *transparent* PVC check valves.
I am getting one of those so next time I'll know for sure.

Luigi

[duraleigh]

Hi, Luigi,

I have never been a fan of check valves......because of the problems they cause.

Would your system function without one?

[Poconos]

As far as I know there are two kinds of check valves. Spring loaded and flap. Spring loaded are closed even with zero flow. Flap require some minimum flow to operate. Spring type may be sensitive to the chemical makeup of the fluid since they probably have a metal spring. As with Dave, I'm not a fan of check valves. They restrict flow to some degree and are prone to problems such as gunk on the sealing surfaces. They do have their use in specific situations but I think they are over prescribed. Just my quarters worth.
Al

[semenzato]

I am not sure why the valve is there but I have a theory. The filter is one story
below the pool and two stories below the solar panels. When the pump stops,
water flows back freely from the solar panels (or they would get scrunched
by atmospheric pressure). Without a valve, this might cause a backflow through
the filter housing and possibly back into the pool through the skimmer.
Having seen how grimey the water is in the dirty side of the filter housing,
I can see how this should be avoided.

Luigi

[semenzato]

In case someone finds this thread:

The culprit was indeed the check valve. The valve has a little round door
(about 1.5") that swings open when the flow is in the right direction, and
closes when there is no flow (by gravity) or when the flow is reversed.
The door has a rubber gasket for better seal. The hinge is none other than
a part of the gasket that sticks out at the top of the door and is attached
to the valve housing. My valve was old enough: the rubber had aged and
the hinge had broken. The door floated freely inside the valve and often
the flow would push it against the outlet, blocking it. (In which case
I doubt that tapping with a 2x4 would have made a difference).

I replaced the valve with an almost identical one, except that this one
is transparent (it cost just a few dollars more) so next time it breaks
it will be easier to diagnose the problem. Finding one that doesn't break
would be nicer, but it may not exist :-)

Thanks to everybody!
Luigi