Can I use an air vent instead of a flange for a shower pump?

[NeilPil]

Hi All, looking for some advice please....

I have a gravity fed system with a Trevi Boost Venturi shower valve and also a basin tap on the ground floor and the hot water supply is delivered over an approx. 20m long 22mm pipe run. The HW tank is on the first floor and this is fed from a CWT directly above in the loft. The problem I have is that the HW supply intermittently stops flowing which I believe is due to low pressure over a long pipe run. It has been suggested that a pump would solve this problem. This would be mounted in the loft near the CWT.

Looking at various negative head pumps they all recommend fitting a flange (Surrey, or other type) to the HW tank (and also a gravity loop in some cases) in the feed to the pump. I understand this is to avoid the possibility of air reaching the pump. My question is whether this is really necessary as it will be a fair bit of work? Could a simple air vent be used in the feed to the pump?

Thanks

 

[Madrab]

Could a simple air vent be used in the feed to the pump?

'Fraid not - The whole point of a flange is to allow the air that's created when the cylinder heats the water to separate and vent naturally up the vent pipe to the CWSC. The pump would pull that air down to the itself too quickly for an auto air vent to remove it if a flange wasn't used. You can up angle the HW supply out of the cylinder and take a tee directly down from that supply to the pump. Only trouble with that is it only works maybe 50% of the time

 

[gas112]

What do you mean by a simple air vent ? if you mean the open vent off the top of cylinder .
If so then a lot of shower manufacturers allow this but after it comes out top of cylinder then the tee the open vent comes off then any tee for a shower supply must be the first branch off and at least 6 inches below the open vent tee .
Also do not have the water in cylinder too hot as it can also cause bubbles(cavitation) in the shower pump

 

[NeilPil]

Thanks for the replies gas112 and Madrab, much appreciated.

Another option is to site the pump next to the shower which would be 15-20m away (pipework length) from the HWC and CWST. Pump manufacturers put a limit on the distance between the pump and the CWST, typically 4m, so seemingly this wouldn't be allowed, but I don't know why.