Pluming overhaul

mas985

TFP Expert
LifeTime Supporter
May 3, 2007
13,825
Pleasanton, CA
Pool Size
20000
Surface
Plaster
Chlorine
Salt Water Generator
Do you still have the old MP?

I am just curious if any of the passages within the valve are less than about 3/4". I did a quick calculation and at 76 GPM, a reduction from 1.5" to about 3/4" that could cause cavitation. From the drawings, nothing looks that small but I don't have a valve that I can actually measure.
 

sefrlw

Well-known member
Mar 25, 2008
130
Wake Forest, NC
Yes I do. I will measure when I get home or in the AM. I do not think anything is that small but you never know. The PVC is 1 3/4 stepped down to the threaded size and the I may get even smaller inside but I do not think it gets as small as 3/4
 

sefrlw

Well-known member
Mar 25, 2008
130
Wake Forest, NC
Been down for a bit. Back issues and trying to get pool ready for a party.

Measurements. Feed from the pump is 1.5 inch in diameter. I do not think it is a design issue. If you look at these pictures you can see the clean area. I think this is where the cavitation was happening on the old one. Why I do not know. The plate of the old one is a mess and when the spider gasket was replaced a few years ago the service guy used PVC cement to glue it in. Well that was not the right thing to do and I think it caused me some of the noise as the PCV ridges that contain the spider gasket were also melted by this and they were no longer nice and smooth. I also had at least two suction side leaks that allowed a lot of air in and could have contributed to the noise prior to the over haul.

Now this is where it gets more interesting. I was having the noise at and below 18 PSI. For the past three days I have been "slamming" the pool. I could not see the bottom on Sunday. Well Sunday I decided to turn off the bottom drain and vacuum the bottom blind. Well apparently I had one heck of a mess down there. Twice during this vacuum session right at the main drain the hose to the vacuum came alive. :) sucked up a large amount of leaves. These leaves are like poster board even wet. The seriously limited the amount of flow through the main drain. This is something that changed during my overhaul. They were not there for days and all of a sudden I was getting air sucked past pump cover gasket. Since clearing these leaves and being able to see the bottom the filtering is working great. No more air past the pump lid water clearing at a rate I would expect and to top it all off. The noise is no longer happening. I had all three returns open and at 14 PSI I have no more cavitation sound.

I am at a loss to explain but my basket is now virtually free of air and the noise is gone. I have yet to take the diffuser out and inspect it also. That will be next if the noise returns after another backwash..

What is the plug for on the back of the backwash valve? The moon shaped hole in the first picture. I also suspect it for turbulence and cavitation.... Maybe others can take theirs apart and see if they also have this wear. I know my new one is cracked but it is not yet worn like this one.... Maybe some caulk in the hole will help? Just a thought.



 

sefrlw

Well-known member
Mar 25, 2008
130
Wake Forest, NC
Well I finally was able to finish the plumbing overhaul. This weekend I put another 3 way diverter in to control between returns and seat jets. I can now turn one or the other on/off. If I need both I can simply remove the stops and select both.....

The noise is no longer there. It had to bee too much flow or cavitation due to too much flow. That is what I am thinking at least. Nice and quiet in the garage now.