shower booster pump air locking

[gbbmotors]

Hi All
I live in a bungalow with hot water cylinder in loft and cold tank mounted approx 40cm above top of cylinder. I have a twin impellor 2 bar pump mounted at base of cylinder, hot feed is from surrey flange mounted on top of cylinder, cold feed straight from cold tank. All feed pipes are 22mm except 15mm pipes down to shower mixer. Since fitting shower the system airlocks every week or so . The cold water tank is definately big enough. Does anyone have a solution. Many thanks George

 

[Burnerman]

I think things would be better with an essex flange, and lifting the header tank higher...guess its pulling air in through the expansion pipe.
John

 

[gbbmotors]

hi burner man
thanks for reply how can air be drawn down expansion - the draw off on surrey flange goes down into cyinder by about 6 inches whereas draw off for taps etc comes from top of cylinder if you see what i mean. Thanks in advance George

 

[Burnerman]

I know exactly what you mean George as I found out the hard way.....these shower pumps can use so much water that not enough can pass through the surrey flange, and the pump finds it easier to draw air rather than water. An essex one gives it more chance as it has a full opening into the copper cylinder and its also lower down.
Thats my theory anyway! Lets see if others chip in.
John

 

[Richard C]

Essex flange is a much better option; does the shower head feed pipework have any up & over loops in it?

 

[gbbmotors]

Thanks John
So to prove your point if I was to open a hot tap when pump is airlocking I shouldn't be getting water out of that tap as water level in cylinder will be below outlet.
cheers George

 

[gbbmotors]

Hi Richard
Yes shower feeds come up from pump about 14 inches go across a couple of feet then drop down to shower mixer. I know this is not ideal but outlet has to come up then back down to mixer.
cheers george

 

[Richard C]

You need to auto vent the tops of any up & over loops to prevent residual air separating out & collecting at the tops of the loops which will eventually air lock the pump. What pump do you have? Some pumps require a non return valve on the pumped HW supply only when up & over loops are used.

Locating the CW pump feed below the mains ball valve feed can also cause aerated CW to be drawn into the pump circuit.

 

[gbbmotors]

Hi Richard
thanks again for your time one very important thing I forgot to mention this air locking only happens when shower has not been used, ie it never happens when shower is in use so I suppose this rules out the surrey flange/essex flange issue/overdrawing supply issue. Yes I will try air vents at top of loops.
By the way do air vents often have to be used when there is an up and over loop.
cheers George

 

[Richard C]

By the way do air vents often have to be used when there is an up and over loop.

You should always fit vents at the top of up & over loops; air rises to the highest point in the system, no vents means nowhere for accumulating air to escape. The lack of a non return valve on the pumped HW circuit can also allow a column of air to form in the vertical pipe run back to the pump when the shower is not used frequently.