Leaking skimmer line

[jan verbeem]

So after 12 years my pool developed a leak, and not just a small one, it loses more than 2" over 24 hours.
My pool is inground, tiled concrete.
I already figured that the leak is in the line from skimmer to pump, but it's all covered by concrete I'm afraid.
The strange thing is though, that if I close the skimmer valve at the pump side, there is no leaking. When I keep the valve open without running the pump, I lose large amounts of water.
When I then start the pump after 24 hours, there is no air in the system. So I'm a bit confused as to why I lose the water in a closed system. My pump is positioned about 50cm above pool level, so if there is a leak in the piping, it must lose water from skimmer and pump side.
I also don't see any wet spots. 2" from a pool 60m² is a lot of water.
I have no real intention to dig up all the concrete, because I have a vacuum feed and a bottom drain to feed the pump.
Any suggestions and opinions are welcomed.

 

[ajw22]

Closing the skimmer valve is like putting your finger over the top of a straw. The bottom of the straw will be open but no water will leak from it since air cannot replace the water and fill the straw.

Similarly, the closed valve does not allow water and air flow back through the pipe.

 

[mas985]

The straw may not be the best analogy unless a section of straw outside of the cup remains below water level and has a leak as it does with the skimmer line. In this case, water would still leak out of the straw even with your thumb on the end of the straw. Water would flow from the cup through the straw to the leak and out via gravity siphon.

The same thing should occur with a leak in the skimmer line between the pool and the valve independent of the valve position as long as the leak is below water level.

Also, if the leak is above water level, only air/dirt should leak in when the pump is off or on.

However, there is a scenario where the valve might make a difference. If there is a leak on the skimmer line that is above the pool water level but below the return level such as with a raised spa, water would need to flow from the return to the leak but if the valve is closed, it would not flow.

When the pump is running, is there still a leak? If so, the leak would need to be on the return side and not the suction side.

 

[mas985]

So I'm a bit confused as to why I lose the water in a closed system.

Because it is not a closed system. The pool water surface is exposed to atmospheric pressure so water can and will always flow from the water level to a lower elevation.

My pump is positioned about 50cm above pool level, so if there is a leak in the piping, it must lose water from skimmer and pump side.

Not necessarily. The return side can also lose water. The way to determine this is if there is still water loss when the pump is on vs off.

 

[jan verbeem]

Not necessarily. The return side can also lose water. The way to determine this is if there is still water loss when the pump is on vs off.

Thanks for your reply, but not sure if I understand your question correctly. Maybe I need more morning coffee.

Is return side the side of the skimmer or the side of the pump/valve?

The valve is inside a tiled pump house, in the middle of a 1-meter vertical pipe. The top of the pipe is a T-junction, to which vacuum feed and bottom drain are also connected to, and each feed is individually controlled by a valve.
From the T-junction it goes down to the pump.
The pump house is bone dry at all times, and the pump has two 3-hour cycles over 24 hours, so I can't answer yet if there is water loss with pump on.
I will check it out soon, please suggest the position of the 3 valves during the test.

Also, would there be a possibility to fix the leak without digging up everything?

 

[jan verbeem]

The way to determine this is if there is still water loss when the pump is on vs off.

I topped up the pool, then let the pump run for 4 hours, drawing water from the skimmer only. There was no visible water loss.
Is this good news or bad?

 

[wireform]

Since you've zero'ed it in thus far go ahead and pressure test that segment of the piping to confirm your results.

 

[jan verbeem]

Since you've zero'ed it in thus far go ahead and pressure test that segment of the piping to confirm your results.

Which segment you have in mind?
I certainly don't have the equipment to pressure test the piping, which is also almost completely covered by concrete.
Definitely there is no leak in the pump house, I can eyeball that easily.
Can you explain to me what my latest test mean? With pump on, no water loss, as soon as I switch off the pump water loss starts.

 

[wireform]

Which segment you have in mind?
I certainly don't have the equipment to pressure test the piping, which is also almost completely covered by concrete.
Definitely there is no leak in the pump house, I can eyeball that easily.
Can you explain to me what my latest test mean? With pump on, no water loss, as soon as I switch off the pump water loss starts.

All you need is two ends of the given pipe at each end. One side would get plugged and the other would have some sort of pressure gauge and a port to pump up the pressure to see if it holds or not. Someone here on the forum may be more helpful to you of how to create one. Firstly good pictures of the equipment pad would be important for better help. Once you have a leak confirmed then you can plan for a fix.

 

[jan verbeem]

Once you have a leak confirmed then you can plan for a fix.

There definitely is a leak. 2" of water disappearing over 24 hours isn't evaporation.
My current question is why there is no water loss when the pump is running.

 

[mas985]

There definitely is a leak. 2" of water disappearing over 24 hours isn't evaporation.
My current question is why there is no water loss when the pump is running.

If the plumbing leaks when the pump is off but not when it is on, it usually means that the leak is on the suction side of the pump. This is because when the pump is running, the pressure on the suction side of the pump is typically below atmospheric through the entire suction side plumbing, which tends to suck dirt/air into the plumbing should a leak occur, while the pressure on the return side is typically above atmospheric so water would tend to leak out should a leak occur in that area.

With the pump off and assuming the plumbing remains fully primed (e.g. no solar and no air entrance), then the pressure in the plumbing is dependent on plumbing elevation vs the water level in the pool. So plumbing below water level has higher that atmospheric pressure and is prone to leaking water out of the plumbing should a leak occur while plumbing above water level is lower than atmospheric pressure and is prone to leaking air/dirt into the plumbing should a leak occur.

When the pump is running, do you see any air in the pump basket or any accumulation of air in the filter (open filter air purge valve)?

Sometimes, the leaks can temporarily seal while the pump is running due to mud sealing the crack and then when the pump shuts off, can then continue to leak.

 

[jan verbeem]

When the pump is running, do you see any air in the pump basket or any accumulation of air in the filter (open filter air purge valve)?

There are no air bubbles visible under the pump cover. My Hayward filter doesn't have an air purge valve, but my chlorinator cell housing is clear plastic, so if there is air in the filter, the cell housing will have an air pocket as soon as I switch off the pump. This is not the case.

If the plumbing leaks when the pump is off but not when it is on, it usually means that the leak is on the suction side of the pump.

This is what I don't really understand. The suction side of the pump should be visible in the pump house, or can it still be somewhere under the concrete outside?

The way it behaves, a check valve below the ball valve on the skimmer line would prevent the water loss when the pump is off, and I would still be able to use the skimmer normally when operating the pump. Would this be a solution, or only temporarily?

 

[mas985]

There are no air bubbles visible under the pump cover. My Hayward filter doesn't have an air purge valve, but my chlorinator cell housing is clear plastic, so if there is air in the filter, the cell housing will have an air pocket as soon as I switch off the pump. This is not the case.



This is what I don't really understand. The suction side of the pump should be visible in the pump house, or can it still be somewhere under the concrete outside?

The suction side of the plumbing goes from the skimmer to the pump. The leak could be anywhere within that area, including the skimmer itself.

The way it behaves, a check valve below the ball valve on the skimmer line would prevent the water loss when the pump is off, and I would still be able to use the skimmer normally when operating the pump. Would this be a solution, or only temporarily?

No, that would not prevent a leak. Water could still travel from the pool, into the skimmer, through the pipe to where ever the leak might be and then out of the pipe.

 

[jan verbeem]

No, that would not prevent a leak. Water could still travel from the pool, into the skimmer, through the pipe to where ever the leak might be and then out of the pipe.

As explained in the OP, when I close the skimmer ball valve in the pump house, there is no water loss with the pump not operative.
So what is the difference with the check valve?

 

[mas985]

As explained in the OP, when I close the skimmer ball valve in the pump house, there is no water loss with the pump not operative.
So what is the difference with the check valve?

That part is inconsistent with the leak on the suction side of the plumbing. I would verify that the leak is indeed on the suction side of the plumbing with a pressure test as @wireform suggested.

 

[mas985]

Is the pool equipment above or below the pool water level?

 

[jan verbeem]

Is the pool equipment above or below the pool water level?

All equipment is above water level

 

[jan verbeem]

That part is inconsistent with the leak on the suction side of the plumbing. I would verify that the leak is indeed on the suction side of the plumbing with a pressure test as @wireform suggested.

But if the leak was not at the suction side I definitely would see water in the pump house, not?

From where the skimmer line enters the pump house through the tiled floor, to the pump is about 2 meters of pipe in total, and everything is powder dry

 

[mas985]

But if the leak was not at the suction side I definitely would see water in the pump house, not?

Not necessarily. You need to remember that there is plumbing that you cannot see. There is return pipe that goes from the pump back to the pool returns which could also leak water. But usually, that would leak water out while the pump is running.

From where the skimmer line enters the pump house through the tiled floor, to the pump is about 2 meters of pipe in total, and everything is powder dry

But there is still skimmer line underground that you cannot see.

I don't know if you have leak detection companies there, but that may be another option.

 

[jan verbeem]

Since I can't find the leak location, I consider emptying my pool indefinitely.
I have a 6 x 11 meter inground pool, and it is more a burden than it is an enjoyment.
The house with pool was built 15 years ago, but I very rarely use the pool, and I'm single. At the same time it has to be maintained, and it actually prevents me from traveling for an extended period of time, because of that.
So I consider from emptying it and covering.
I have read on the internet about pools that get lifted out of the ground, or get cracks in the floor, because of the groundwater.
My pool is tiled concrete.
What are the risks here, considering I live in a flood free area. I have a 35 meter deep borehole, and I have to put a timer on it, otherwise the pump runs dry after 10 minutes.