What size DE Filter?

JamesW

TFP Expert
Mar 2, 2011
21,049
The drain plug threads are 1/4" NPT. Can the gauge screw into the drain plug?

What is the gauge model number?

Note: Don't overstress the drain plug threaded hole as it might crack the port.
 

BlueBaron

Bronze Supporter
Aug 27, 2020
47
Orinda, California
The drain plug threads are 1/4" NPT. Can the gauge screw into the drain plug?

What is the gauge model number?

Note: Don't overstress the drain plug threaded hole as it might crack the port.
The gauge is Robinair RAVG-1. It has a 1/8 inch male NPT threads and I have a 1/4 inch adapter that fits nicely into the port under the pump filter basket. Thank you again.
 

BlueBaron

Bronze Supporter
Aug 27, 2020
47
Orinda, California
Assuming the numbers are accurate, the suction seems to have a problem. The head loss on the suction seems to be about equal to what you would get with 100 feet of 1.5” pvc pipe, which is way too small for the suction of the pump.

What is the actual plumbing size and length of the suction plumbing?

Are you pulling from 1 or two skimmers?

Are you pulling from the main drains at the same time?

You might have a clog in the suction plumbing or baskets or maybe a clog in the impeller.

You might need to get a vacuum gauge to check the suction pressure. You can screw it into the drain plug port of the pump. It’s 1/4” NPT thread. Just don’t over tighten the gauge or it will crack the drain plug hole.

What is the actual model number (part number) from the front barcode sticker on the pump?

The silver sticker should have a barcode, a date and a P/N (part number).
I figured out something new today. My underground plumbing is all 1.5”. The above ground plumbing is 2”. I assume that is why my flow is so low?
 

JamesW

TFP Expert
Mar 2, 2011
21,049
How many 1.5" pvc pipes are feeding the pump on the suction side?

How long are the pipes?

Did you get a suction vacuum pressure?
 

BlueBaron

Bronze Supporter
Aug 27, 2020
47
Orinda, California
How many 1.5" pvc pipes are feeding the pump on the suction side?

How long are the pipes?

Did you get a suction vacuum pressure?
Thank you. I still have not gotten suction pressure because I am getting my gauge repaired. The pipes on the suction side are 45 feet. (That is the distance from the skimmer to the pump).
 

BlueBaron

Bronze Supporter
Aug 27, 2020
47
Orinda, California
There are two pipes (that I can see above ground) feeding the pump. One is the return from the hot tub which is built into the pool (and there is a valve that we can adjust to change whether the pump is pulling from the pool or the hot tub or both) The other pipe other comes from the pool itself. We believe that the return from the pool comes from the skimmer and the drain at the bottom of the pool. I just took a picture of the bottom kimmer and I notice it has some of a crescent shaped piece of plastic at the bottom. I dont know what that is. Thanks for your help!

IMG_4B1C7379F0D0-1.jpeg
 

JamesW

TFP Expert
Mar 2, 2011
21,049
I think that the pipes are undersized and they might be partially clogged.

You probably need to keep the flow rate down as much as possible and maybe have the lines checked for blockages.
 

BlueBaron

Bronze Supporter
Aug 27, 2020
47
Orinda, California
I think that the pipes are undersized and they might be partially clogged.

You probably need to keep the flow rate down as much as possible and maybe have the lines checked for blockages.
I am going to see if I can look for clogs in the lines today. Do you know what the threaded pipe is for at the bottom of my skimmer? Or the semicircular pvc with the hash marks on it? Thanks again for your help.
 

BlueBaron

Bronze Supporter
Aug 27, 2020
47
Orinda, California
I am trying to learn about my old pool. My skimmer has a single hole at the bottom. There is a threaded pipe that comes out of the hole. There is also a semicircular shape that has hash marks. Can anyone help me figure out what the threaded pipe is for and whether this skimmer is adjustable somehow? Thanks very much!


IMG_0771.jpeg
 

Jimrahbe

Mod Squad
TFP Expert
LifeTime Supporter
Jul 7, 2014
19,377
Bedford, TX
Blue,

Many old pools have their main drain plumbed back to the underside of the skimmer.. Most have two holes, but some, like yours only have one hole.. My guess is that there used to be a swinging "flap" that you could set for how much water you were sucking from the main drain.. The hash marks kind of held the flap in place and showed how much it was open or closed..

I don't know that as a fact for your specific skimmer, but I have a similar skimmer at a rent house pool...

Thanks,

Jim R.
 
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BlueBaron

Bronze Supporter
Aug 27, 2020
47
Orinda, California
The available information is indicating that the suction side has excessive restriction.

I would get rid of the check valve. I don't see any reason to have it there and it might be clogged with debris.

Does the pump get really loud at full speed like it's cavitating?

You can put a Jandy check valve between the pump and filter if you want, which I would recommend if you switch to a DE filter.

Remove the check valve and recheck the readings for flow to see if there is any improvement.
Hello James, I cleaned up some of the plumbing and I got rid of the check valve as you suggested. I also was able to measure vacuum. The new numbers (without the solar are:

RPM. Filter Pressure. GPM. Vacuum in Hg

3450. 18. 62. -24
3110. 18. 60. -22
2350. 12. 40. -11


What do you think? Thanks for your help. @JamesW
 
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JamesW

TFP Expert
Mar 2, 2011
21,049
The numbers are a little bit better, but the suction is roughly the equivalent of 100 feet of 1.5" pvc plumbing.

Unless you can figure out how to improve the suction side, I would try to keep the flow rate below 40 gpm at all times.

I would try to keep the flow rate as low as possible while still providing the necessary flow for each function such as solar, skimming, SWG etc.

Overall, the system is excessively restrictive and inefficient.
 

JamesW

TFP Expert
Mar 2, 2011
21,049
If you check the total head at the speed curve, the numbers don't exactly match up.

For example, at 3,450 rpm, the total head is measured at about 69 feet. The flow at 69 feet of head should be about 120 gpm at 3,450 rpm.

The measured flow is 62 gpm, which is significantly less than expected. For 62 gpm, the head loss from the curve is about 91 feet vs. the measured head loss at 69 feet.

For 3,110 rpm, you're getting 67 feet and 60 gpm. 67 feet would be about 75 gpm.
60 gpm would be about 73 feet of head.

For 2,350 rpm, you're getting 40 feet and 40 gpm. For 40 feet of head, the flow would be about 55 gpm. For 40 gpm, the head loss would be about 42 feet.

At lower speed, the numbers are not too far off.

At full speed, the pump is possibly cavitating.

Definitely keep the flow below 40 gpm unless you get the plumbing improved.

How much flow does the solar need?
 

BlueBaron

Bronze Supporter
Aug 27, 2020
47
Orinda, California
If you check the total head at the speed curve, the numbers don't exactly match up.

For example, at 3,450 rpm, the total head is measured at about 69 feet. The flow at 69 feet of head should be about 120 gpm at 3,450 rpm.

The measured flow is 62 gpm, which is significantly less than expected. For 62 gpm, the head loss from the curve is about 91 feet vs. the measured head loss at 69 feet.

For 3,110 rpm, you're getting 67 feet and 60 gpm. 67 feet would be about 75 gpm.
60 gpm would be about 73 feet of head.

For 2,350 rpm, you're getting 40 feet and 40 gpm. For 40 feet of head, the flow would be about 55 gpm. For 40 gpm, the head loss would be about 42 feet.

At lower speed, the numbers are not too far off.

At full speed, the pump is possibly cavitating.

Definitely keep the flow below 40 gpm unless you get the plumbing improved.

How much flow does the solar need?
Extremely helpful. The solar needs 28 gpm. A few questions/observations:

1) Why below 40 gpm? I assume that is for effiency on the curve.

2) Now that I understand what cavitation sounds like, the pump does cavitate at 3450 and stops at 3100.

3) Do my vacuum numbers tell you whether my pump appears to work properly

4) When I change my valves to pull from the spa only, the gpm doubles from what it is when I pull from the pool.

Thanks for your help.
 

JamesW

TFP Expert
Mar 2, 2011
21,049
The pool suction has too much restriction.

Based on the numbers, it really doesn't efficiently support more than about 38 gpm.

The power required to move water through the system increases exponentially by a cube factor.

For example, doubling the speed increases the power usage by 8 times.

So, it's always more efficient to move the water as slowly as possible.

It's hard to evaluate the pump when the plumbing is undersized.

I suspect that the pump is probably ok and most of the issue is with the suction plumbing.
 

BlueBaron

Bronze Supporter
Aug 27, 2020
47
Orinda, California
The pool suction has too much restriction.

Based on the numbers, it really doesn't efficiently support more than about 38 gpm.

The power required to move water through the system increases exponentially by a cube factor.

For example, doubling the speed increases the power usage by 8 times.

So, it's always more efficient to move the water as slowly as possible.

It's hard to evaluate the pump when the plumbing is undersized.

I suspect that the pump is probably ok and most of the issue is with the suction plumbing.
 

BlueBaron

Bronze Supporter
Aug 27, 2020
47
Orinda, California
Thanks for another helpful reply. If it is a clog in the pipes, would I get someone to run a snake? If so, its hard to see where you would run a snake. Through the little hole in the skimmer? Through the drain at the bottom of the pool (not easy with a full pool)? Try to go in the other direction (cut the return from the pool and go that way?