Cavitation and Surrey flange

[PJK]

I have had a power shower for about seven years and am on my third pump at the moment. The original pump was made by New Team and the replacements have been the same for ease of replacement. I suspect that the short lifespan of the pumps is because of cavitation in the hot side which I believe is why when the shower is first turned on there is a rise in the note from the pump as if air is being sucked, which settles again after 15 seconds or so. There are no leaks in the system. The hot side comes from the cylinder via a Surrey flange and I wonder whether anybody knows which connection on the flange normally goes to the dip tube. At the moment the rest of the hot water is connected to the top or vertical connection and the shower to the side opening. It did occur to me that if these were the wrong way round it might give rise to the symptoms above. Any other suggestions also welcome, and apologies for a long winded post. Many thanks.

Peter

[Capitol]

Your connections are correct. However, unless you have a good 28mm cold supply into the base of the cylinder, I would not be surprised by cavitation. You may be able to reduce the effect by adding a restrictor in the pump outlet, to limit the flowrate. Hopefully the pump input is plumbed in at least 22mm and there is not a bypass on the pump? Another way to increase the available supply to the pump is to fit both a Surrey and Essex flange to the tank.

Hope this is helpful.

Regards Capitol

[Aidan]

PJK wrote: I suspect that the short

Water temperature? Should be 60 degC, not more than 65 degC.

Isolating valves? Should be full-bore ball valves or gate valves, offering little restriction.

Strainers/filters on the pump inlet? Ensure they're clean.

[OldBill]

The side is the correct connection for the shower. It may be significant that at least one pump manufacturer does not recommend surrey flanges.

[Allan Plant]

The brushes have worn out. New brushes from NewTeam f.o.c but seals are £10 per set, each pump end. Assumes the commutator is ok. Almost complete strip down to fit brushes. Just repaired my Varispeed 50. Pumps last me 3 years on average.

1st 'repair' was new pump, 2nd 'repair' recon pump from NewTeam (no longer available) 3rd 'repair' brushes. Next repair will be Stuart Turner pump!

Al

[Mike Smith]

Hi

If you have had the same cylinder for the whole time you have had the pumped shower, then it might be an idea to replace the cylinder with one that has a 'secondary return' connection fitted. You can connect the pumped shower outlet to this connection without using any special connectors and not draw air into the pump.

If you have agrade 3 cylinder (10 m working head or less) then it shouldnt be too expensive and will eliminate any possibility of air getting to the pump.

Hope this helps

Mike

[tarquinlinbin]

Never really been into Surrey flanges for pumped showers,Essex is the sure way to make sure it all works ok,,

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[Ian_m]

Are you sure they are connected right ?. My mates power shower in the house he bought was installed on the wrong outlet of the flange. He suffered from sometimes complete lack of HW from the pump. He got a plumber to install an air relief valve in the hot feed to the pump, which did improve things alot.

Anyway same plumber was back for another job, kitchen re-plumb, when, working on the HW tank (putting 22mm hot feeds to kitchen to replace inadequate 15mm), removed the flange and discovered the shower pump hot feed was on the wrong connection off the flange. Thus the hot loop to the pump was collecting all the air rather than the expansion pipe to loft.

A quick replumb later and shower has been fine for the last couple of years, no air, no cavitation in pump.

[PJK]

I wasn't sure which is why I asked the question, but from other replies it would seem that the solution lies elsewhere. Thanks to all for the responses and suggestions.

Peter.