by Sean Griffin, January 18, 2010
Air Leaks in the Lines
Often when we think of a leak in a swimming pool we automatically assume it is water dripping from a broken pipe, water escaping at a loose connection, or moisture seeping into the surrounding ground. In some cases these drips are not only water leaks but transform into air leaks when the system is shut down. It is also possible for air leaks not to drip but serve as an open air vent, sucking in air when the system is running and allowing air to fill the plumbing and/or pool components when the system is off.
The sometimes elusive air leak can be more dangerous than a water leak. As air is sucked back into your system the pump can lose prime. When the system is turned back on it puts extra stress on the pump and can even lead to melted/warped components. In short, an air leak can damage plumbing and pump components leading to costly repairs. To prevent these drastic damages all leaks or loose connections at the equipment pool pad should be repaired promptly and correctly.
Air leaks occur in the plumbing loop when the system or parts of the system are located above the water level of the pool. Naturally gravity will force water back to the lowest elevation possible. This is prevented by a closed plumbing loop. A simplistic model of this can be made using a cup of liquid and a drinking straw…...in fact you’ve probably already done it. If your straw is submerged in your glass you can put an air lock on it using your finger by covering the hole. Lift the straw out of the water and the water remains in the straw until you remove your finger. If the structure of the straw is cracked air will slowly fill the straw. An air leak in pool plumbing is the same but on a larger scale with several other forces at play.
As mentioned air leaks are typically associated with above pool level plumbing. On the suction side of the pump these air leaks may or may not drip. When the system is on and “prime” is achieved, air will be sucked into the line and work its way through the system until finding an escape. This can be at the pool return or any other opening succeeding the pump strainer housing or volute. You might notice air bubbles streaming out of the closest return to the equipment or highest elevated return making a gurgling sound as air rises to the surface.
Plumbing and pool components after the pump are pressurized and more likely to leak water as well as air although in rare cases they may not. For example, a swimming pool that I maintained had a tendency to create a vortex in the skimmer because it lacked a skimmer weir and had excessive suction due to a collapsed drain line. The air would funnel down into the skimmer and work its way through the plumbing and through the pump, collecting at the filter. There was no apparent leak once the system was running but would constantly loose prime when system shut off. In this case once a weir was put in the skimmer, the leak at the top closure dome of the filter started to seep moisture and the air leak was located and fixed. This was kind of a tricky one, but trust me plumbing leaks can become way more complex than that. There are several variables that should be taken into consideration when attempting to locate an air leak; what components are included within the plumbing loop, type of plumbing used under-ground, elevation of equipment, and more. Having the patience and understanding needed to locate and fix your leak will save you some time and money.
The first step in fixing an air leak is to locate it. The easiest way to pinpoint the problem is by using your given senses and incorporating some detective skills. The obvious leak drips, sprays, or allows moisture to be visible. At times it can be hard to determine exactly where the moisture is coming from. Keep in mind water will run to the lowest point before dripping. As previously stated the leak may not have any “moisture” characteristics.
For those hard to find water leaks and those elusive air leaks we can shut down the equipment once it has achieved prime and look, feel, and listen for indications to help us narrow it down. When the pump is shut down and the filter is pressurized back pressure is created which can sometimes cause a spray of water to momentarily jet out. Another method used, mainly to locate leaks in a gas line and finding a hole in a car tire, involves using a “sudsy” or “soapy” solution. Sprayed on a suspected area escaping air will form bubbles.
Another method is to isolate and pressurize the suction side manifold. Sound complicated? It is more involved, but it takes only a few minutes to set up. Pressurized water is put into the suction side of your pump. This is achieved by having an external pump hooked up to the suction side of pump or a “drain king” which fits on the end of any garden hose. Typically this method begins introducing pressurized water at a skimmer with a drain king or other "sealable" apparatus. The other end of the pipe is also sealed off, either before, at or after the pool pump. A plug into the front of the pump, from the inside is one way to block the water. Suction valves can be closed, or even return valves can be closed. A multiport valve can be put on the Closed position. Now that the pipe is isolated, or closed on both ends, and it is under pressure (it's normally under suction), we can look for any drips. Look around valves, connections, and all around the pump.
You don't need to check after the pump for an air leak, usually. After the impeller, the pressure on the line goes from negative to positive. Or, from suction to pressure. After the impeller, a void will leak water - because it's under pressure. Before the impeller, a void will suck air in, or leak air, because of it's "negative suction pressure". For obvious reasons lines under the ground will prevent us from locating visually. If the leak is suspected to be buried a pressure test can be performed to locate.
Locating the suspected air leak is only half the battle. Once you determine where system has become compromised we need to replace or repair the correlating component. Every connection at the equipment is a possibility for a leak as well as all plumbing lines. The repair depends entirely on what is leaking. Some common occurrences are:
-Threaded connection on pump- (this connection is normally sealed by Teflon tape). Excessive vibration and heat associated with the pump can often create an air/water leak at this point.
-Poly piping/fittings- Older pool construction utilized poly piping that connected to rigid plumbing using poly fittings and hose clamps. These clamps often need to be retightened or repaired.
-Drain plugs- All pool equipment is equipped with drain plugs located at the base or lowest part of the unit. During the winterization process they are removed then reinstalled when opening. Some drain plugs use an o-ring which can be compromised from removing and installing repeatedly. Some pool companies will use Teflon tape as an ineffective alternative. When the plug is removed grit can sometimes prevent a proper thread seal.
-Multi-port/push-pull valve- used to control the flow of water it is used to open/close the waste line. If the seal is not 100 % water will escape and air will get in lines when system is down.
The list goes on and on. Remember any component is a potential leak.
I have seen several methods used as a temporary fix. Air leaks, as discussed, are typically on the suction side of the pump. I have attempted to do several “quick fixes” such as silicone, epoxy resin, plumbing glue, etc…. These are only temporary. A band aid is never the way to go with a suction leak. When dealing with these leaks remember they have the potential of “melting” your pool equipment, or worse, building enough air pressure to blow off the filter lid. Bad plumbing connections or damaged pool equipment components should be replaced.