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#1 DavidJ

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Posted 01 October 2010 - 02:36 PM

I am trying to determine if there is a leak on the suction side of a pool pump. The pump in this case is a Pentair Intelliflo VS 4X160 (great pumps in my opinion). It is probably 25' from the closest end of the pool. Elevation wise, it is probably about 2' above the pool water level. On the suction side it has a skimmer, a bottom drain and a vacuum port with dedicated old red-handled plastic ball valves. Isolating any of these doesn't materially change the amount of water in the strainer but it is possible that all three valves allow air in. The water coming out of the pump goes to a cartridge filter, heat pump, Chlorine generator and pool.

I have a few questions that will hopefully help me understand what to expect better. I have read some of the suggestions here as to common sources of air intrusion.

1. Should the clear strainer lid on the pump always be solid water with no air visible under the lid? On this pump, the clear strainer is not smooth on the bottom. It was molded in such a manner that it has it has pockets that can trap air. I frequently see air compartmentalized under the lid in these pockets. At the lower speeds the basket might only be partially filled. Should that be expected? I see more air than you would expect, even at medium speeds. I'm sure that I've seen pumps at other people's homes where there is no visible air. How long should it take to flush out all or most of the air from the strainer basket once water starts flowing, after you've removed the lid and had to reprime?

The crazy thing is that I don't really see air coming out the discharge line to the pool. I don't know if it get's trapped in the Hayward cartridge filter housing. Will air pass through the filter if the water hasn't been displaced with air yet? I need to monitor that more carefully and see if it is filling up. Those filters have a manual air bleed valve on the top of the filter.

2. How much air infiltration does it take to measurably degrade the pumps ability to move water? Someone told me that an old professional trick was to light a cigarette near each potential source of leakage (on a very calm day) and see if it gets sucked in. Does that work and would it detect a tiny, but suction reducing, leak?

3. Are there any other ways to pinpoint the source of a suction problem?

Thanks for your insight and suggestions at isolating a problem.

#2 Pool Clown

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Posted 01 October 2010 - 05:03 PM

I see this all the time with these 4 X 160 pumps (mine included). If you had no air related problems before the new pump went in, I doubt that you have an air leak. Usually, if you have an air leak, you will eventually get air coming out of the return lines. You can try opening the filter air relief and see (after the initial air is bled out of the tank) if you get "spitting" (occasional air) that won't stop, then i might investigate further. You can also try turning up the rpm's on the pump to see if the pot will glass over, but this will not always work to completely fill the pot.

As far as the cigarette trick, never heard of it. I use a garden hose with the water turned way down and flood the area in question with the water and the pot fills up when you flood the leak, but as stated before, this trick will probably won't work with this particular pump as the pump runs normally with a half (full) pot or more.

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#3 PoolSpaGuy30

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Posted 02 October 2010 - 02:21 AM

some air bubbles are not uncommon within the pump basket, things to look for "above ground" meaning at your equipment would be things such as: faulty glue joints (use water mixed with dish soap to find these), leaky valves for example do you have gate valves? or perhaps pvc union valves that may need to be tightened? how about the fitting at the front of your pump which could be loose or need to be removed to apply some silicone or teflon tape, or if it is an O-Ring seal the O-Ring itself could be dried out, the pump lid O-Ring could also cause air leaks, a cracked pump lid is another obvious thing to check as well as any drain plugs on the pump. If everything is "solid" at the equipment you could be dealing with something underground, a lot of older pools were plumbed with poly. pipe fitted with hose clamps so sometimes air can be drawn in through an "aged" fitting. Pin hole suction leaks are also common not causing much water loss but can cause air bubbles. From experience I know air bubbles drive some customers absolutely nuts and even though they were not losing water I've had customers spend thousands of dollars to pressure test, re-plumb skimmer, vac, main drain lines, etc. just to get rid of those air bubbles. Any other questions just ask :D

edit: if you could provide some close of pics of your setup (valves, pump, filter, etc. I could visually attempt to help you out with anything above ground
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#4 Pool Clown

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Posted 02 October 2010 - 12:19 PM

Any other questions just ask :D

I have a question, Have you dealt with these particular pumps? Because if you had, you would know that these pumps have that inherent problem.

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#5 frankym

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Posted 03 October 2010 - 08:11 AM

I haven't delt with these pumps, however, I have delt with air leaks and the flooding of suspected areas with water works well. My concern with air leaks would be, How much air is considered detremental to the pump or ceramic shaft seal or other attached equipment? I would think if the output pressure is still being maintained, the cermic seal would still be okay. As fae as other equipment I don't have any information. Please comment.

#6 Pool Clown

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Posted 03 October 2010 - 09:02 AM

Water is what keeps the seal from generating too much heat and failing. If there is water moving though the pump, the seal is getting the cooling it needs.

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#7 dmorton

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Posted 04 October 2010 - 09:11 AM

Try checking the impeller. had a problem like this a few weeks ago and solved with he help of the guys on here.

i was getting air bubbles and had no pressure, i changed out the seals, o-rings.
turned out to be a clogged impeller, try to inspect it.

good luck

#8 DavidJ

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Posted 05 October 2010 - 09:09 AM

I see this all the time with these 4 X 160 pumps (mine included). If you had no air related problems before the new pump went in, I doubt that you have an air leak.


Well I'm glad to hear that the partial filling of the strainer basket is not indicative of a problem, and that you've observed this multiple times. I was thinking that that was a pretty good sign of a compromised suction line. Are these Intelliflo models the only ones that behave that way? It is my understanding that the wet end of the pump is the same as some of their other models. Certainly the generally slower speed that people often run these will make it less likely that they will fill up.

In this case there are no visible bubbles coming out of the pool and there doesn't seem to be much (if any) air building up inside the filter. Will a suction leak of any size materially affect the pump performance?

Thanks again for describing and relating your experience with this particular pump. It may have kept me from pulling my hair out trying to eliminate that strainer basket air when it should apparently be considered quite normal (with these particular pumps).

#9 DavidJ

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Posted 05 October 2010 - 09:18 AM

some air bubbles are not uncommon within the pump basket, things to look for "above ground" meaning at your equipment would be things such as: faulty glue joints (use water mixed with dish soap to find these), leaky valves for example do you have gate valves? or perhaps pvc union valves that may need to be tightened? how about the fitting at the front of your pump which could be loose or need to be removed to apply some silicone or teflon tape, or if it is an O-Ring seal the O-Ring itself could be dried out, the pump lid O-Ring could also cause air leaks, a cracked pump lid is another obvious thing to check as well as any drain plugs on the pump. If everything is "solid" at the equipment you could be dealing with something underground, a lot of older pools were plumbed with poly. pipe fitted with hose clamps so sometimes air can be drawn in through an "aged" fitting. Pin hole suction leaks are also common not causing much water loss but can cause air bubbles. From experience I know air bubbles drive some customers absolutely nuts and even though they were not losing water I've had customers spend thousands of dollars to pressure test, re-plumb skimmer, vac, main drain lines, etc. just to get rid of those air bubbles. Any other questions just ask :D

edit: if you could provide some close of pics of your setup (valves, pump, filter, etc. I could visually attempt to help you out with anything above ground


I'm curious how soapy water would help with a vacuum leak. I can understand if air is blowing out but wouldn't think you could see much in a vacuum situation.

You list a number of important things to check for. In this case, since we don't seem to have much if any bubbles, I think we were probably just led astray by the excess water in the strainer basket with this particular pump. There are three older PVC ball valves that control water coming from the skimmer, main drain and side pool port respectively that should probably be replaced, just to be sure. Right now they are plumbed so that they could all three be closed which seems like it is asking for trouble, as opposed to using a three way between the side port and the skimmer so that no one could accidentally cut off complete flow to the pump.

Thanks for your help.

#10 Pool Clown

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Posted 05 October 2010 - 03:26 PM

I think the reason is because the impeller on the 4X160 is a 3 1/2hp, and the vanes are so large that with decreased rpm's the impeller never "gets the water going" enough to glass over the pot. And if your plumbing isn't rated for a 3 1/2 hp pump, the plumbing won't allow the increased flow necessary to glass over. I have 2" plumbing, and if i ramp the pump up to just before it begins to cavitate, i can get the pump to run with a full pot. But that ends when i open it up to clean the strainer bskt.

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#11 DavidJ

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Posted 05 October 2010 - 05:14 PM

I think the reason is because the impeller on the 4X160 is a 3 1/2hp, and the vanes are so large that with decreased rpm's the impeller never "gets the water going" enough to glass over the pot. And if your plumbing isn't rated for a 3 1/2 hp pump, the plumbing won't allow the increased flow necessary to glass over. I have 2" plumbing, and if i ramp the pump up to just before it begins to cavitate, i can get the pump to run with a full pot. But that ends when i open it up to clean the strainer bskt.


So if you were to truly max one of these out, what size pipe would it take to do it justice? I realize that this is not wise as you would greatly compromise the efficiency running it at the limit of its capabilities, but an interesting thought nonetheless. Did I read somewhere that California is now dictating larger pipes on pool installations because of the efficiencies of bigger pipe?

Do you know what RPM you are at where it starts to cavitate with 2" pipe? How can you tell that it is cavitating or starting to cavitate? I've never ran one up that high.

#12 Pool Clown

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Posted 05 October 2010 - 07:28 PM

So if you were to truly max one of these out, what size pipe would it take to do it justice? I realize that this is not wise as you would greatly compromise the efficiency running it at the limit of its capabilities, but an interesting thought nonetheless. Did I read somewhere that California is now dictating larger pipes on pool installations because of the efficiencies of bigger pipe?

2 1/2 to 3" depending on the length of the run. And Yes, also sweep 90's.

Do you know what RPM you are at where it starts to cavitate with 2" pipe?

The point at which you begin to cavitate, is different from plumbing system to plumbing system. But again, it boils down to length of pipe.

How can you tell that it is cavitating or starting to cavitate? I've never ran one up that high.

Run the pump up till it sounds like someone threw a hand full of gravel into the pump. Some people think that is the point, others think that it is just before that sound. But you don't want to make it do that for long periods of time any way.

BTW, there are calculations that you can do, to get precise answers to your questions, but i'm too old to remember. I figured that you arent going to dig up your yard to replace all your pipe at this point anyway.

These pumps work real well for water features, waterfalls especially. It gives you the ability to dial in a speed that looks good, or set different speeds for the (waterfall) sound.

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and Paramount pool cleaning systems.


#13 DavidJ

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Posted 06 October 2010 - 02:39 PM



So if you were to truly max one of these out, what size pipe would it take to do it justice? I realize that this is not wise as you would greatly compromise the efficiency running it at the limit of its capabilities, but an interesting thought nonetheless. Did I read somewhere that California is now dictating larger pipes on pool installations because of the efficiencies of bigger pipe?

2 1/2 to 3" depending on the length of the run. And Yes, also sweep 90's.

Do you know what RPM you are at where it starts to cavitate with 2" pipe?

The point at which you begin to cavitate, is different from plumbing system to plumbing system. But again, it boils down to length of pipe.

How can you tell that it is cavitating or starting to cavitate? I've never ran one up that high.

Run the pump up till it sounds like someone threw a hand full of gravel into the pump. Some people think that is the point, others think that it is just before that sound. But you don't want to make it do that for long periods of time any way.

BTW, there are calculations that you can do, to get precise answers to your questions, but i'm too old to remember. I figured that you arent going to dig up your yard to replace all your pipe at this point anyway.

These pumps work real well for water features, waterfalls especially. It gives you the ability to dial in a speed that looks good, or set different speeds for the (waterfall) sound.


Was your answer about 2.5 or 3" pipe referring to California's requirements or what it would take to max on of these pumps out?

Thanks to you and others for your responses here.

#14 quantumchromodynamics

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Posted 06 October 2010 - 06:22 PM

So if you were to truly max one of these out, what size pipe would it take to do it justice?

The pump can get up to about 150 gpm at full speed. I recommend that the water velocity in the suction pipe should not exceed 7 feet per second, and the head loss should not exceed 12 feet. Note: Vapor cavitation does not occur until about 30 feet of head loss.

Running at full speed requires suction piping of at least 3-inch I.D, which is good for a pipe length up to 235 feet of straight pipe (12 feet of suction head loss). A total straight pipe PVC length of 585 feet would create about 30 feet of head loss.

Here is a head loss and velocity calculator.

Fittings create more head loss than straight pipe. Fitting can be converted into straight pipe length equivalents. Here is a Friction Loss Equivalent Length - feet of Straight Pipe (ft) chart. For example, one 3-inch 90-degree elbow is equivalent to 7.9 feet of straight pipe as far as head loss is concerned.

If you had a 3-inch pipe with (5) 90s, then the maximum length of pipe would be 235 - (5 x 7.9) = 195.5 feet.

For 2-inch PVC, vapor cavitation (30 feet of head loss) wouldn't occur until the total equivalent length of straight suction pipe got to about 85 feet. 34 feet of straight PVC would cause about 12 feet of head loss. 2-inch pipe should not be used except for very short sections of straight pipe, and definitely no 2-inch 45s or 2-inch 90s.

For 21/2-inch PVC, vapor cavitation (30 feet of head loss) wouldn't occur until the total equivalent length of straight suction pipe got to about 204 feet. 81 feet of straight PVC would cause about 12 feet of head loss. 2.5-inch PVC should also be kept to a minimum. 2.5-inch 45s can be used, but 90s should not be used.

Note: There are two types of cavitation. The first one is dissolved gases cavitation and the second is phase change cavitation (vapor cavitation). Dissolved gases cavitation occurs when the pressure in the water is low enough to make a significant portion of the dissolves gases come out of solution. Vapor cavitation occurs when the pressure in the water is low enough to cause the water to phase change into a gas.

You can see the same thing happen when you boil a pot of water. As the water heats up, you will see small bubbles begin to appear. The first bubbles to appear are the dissolved gases coming out of solution. This happens before the water begins to boil. When the water temperature gets to 212 F, additional heat will cause the water to phase change into a gas.

Good plumbing design and engineering are also critical to avoid excessive turbulence. Excessive turbulence can cause localized low pressure cells, which can contribute to the risk of cavitation. You should avoid the use of excessive 90s, especially near the pump or near each other.

Due to various factors, such as turbulence and gaseous cavitation, cavitation can occur at substantially lower pressure than calculations predict for the suction head loss. This is why it is important to include safety factors such as limiting the water velocity and the head loss.
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