Air getting into pumped shower

[jonw]

Hi all,
I have a pumped shower in the ensuite and have recently tee’d off the pumped H+C to feed an over-the-bath-shower.

Since I did this the problem is that when a hot water tap is open and closed briefly (which is not on the pumped plumbing circuit) it causes the pump to run briefly. I think this is because I have air in the pipes after the pump. I can clear the air out which solves the problem but it returns after the ensuite shower has been run for a few showers. I think that I might be getting air somehow sucked into the pipe work from the shower valve due to suction at the Tee coupling that I added. I fed the tee coupler at one end; the straight opposite side went to ensuite and 90 degree bend to over-the-bath-shower. My theory is that when the ensuite shower is running it sucks water out of the over-the bath-shower valve and eventually air gets in.

Questions
1. Excuse the pun but.. does my theory hold water?
2. Would it be better to feed the tee from the centre (rather than one end) so that both the ensuite and the over-the-bath showers both effectively have 90 degree bends. Would this solve the problem of sucking air into the system
3. Or is it best to fit an NRV after the tee.
4. Why does it only happen on HW and not CW as well.

More info
It is a salamander whole house pump that up until recently only fed the ensuite shower. The pump has been correctly installed (7 years ago) sited next to HW tank, with surrey flange, and the pump has its own feed from CW tank. It’s all in 22mm copper pipe work. Before I did this mod there have never been any problems with air in the system.

Cheers Jon

 

[Richard C]

I doubt your sucking air into the system via the shower valve; did you introduce any up & over pipe work on the new over bath shower? If you did, it’s more likely to be accumulation of what little air is still in the H/W from the cylinder. Up & over pipe work needs to be vented at the top of the loops to avoid this very problem. Essex flanges are also by far the best for eliminating air in the H/W supply, are the preferred flange of Salamander & most other pump manufacturers.

I assume it's a positive head pump fitted at the base of the H/W cylinder? A schematic of both sets of pipe work, roughly to scale with some critical dimensions between pipework & tanks might be useful.

 

[jonw]

Thanks for the reply. Attached is a hand drawn schematic. Interestingly enough when I turn the isloation valves off in the bathroom the problem does not occur, seems to impy thats where the air is which is why I suggested perhaps thats where the air gets in (not sure how though). Makes no difference if i turn the ensuite isolation valves off or not.
Pump is located at base of cylinder. Notice the loops immediately after the pump, do I need to vent these? They have not been a problem before.
I could probably add some photos of the pipe work if that would help. Cheers View media item 31952

 

[digdilem]

Just a thought. Try turning the water temp in the hot water tank down by 5 or even 10 degrees on its thermostat.

If it's too hot, it can cause cavitation which can lead to air in the pipes even with a surrey flange fitted.

I can't see anything wrong with the layout and in fact run a near identical setup here in my bungalow. (just without the ensuite shower)

 

[jonw]

thanks for your suggestion. I already set the temp lower to 55 deg C last week after reading about it somewhere on this forum -although it was set to 60 deg c before I made the changes there was no problem with air.

The new bit in the diagram is just inserting a the tee for the bathroom into the existing pipe work. The rest is the original pipework.

 

[digdilem]

Ok, certainly 55 should be cool enough.

Can't think of anything obvious, so have to agree with your conclusion - that somewhere it's sucking in air through a joint or tap.

 

[Richard C]

Sorry not been able to get back earlier, unusually busy t the moemnt. Where is the take off for the un-pumped HW circuit?

 

[jonw]

Richard, from the top of the tank. The surrey flange has two outlets - the one for the pump comes out horizontally and the top vertical one for the vent and other hw services.

I also have another theory. The T for the new connection to over-bath-shower is pointing upwards. As the water rushes past when the ensuite shower is used will cause some turbulence at the coupling and any air (assuming some coming through from pump) will bubble up the vertical T and eventually collecting enough air to cause this problem. It's definitely a new problem caused by adding the T, when I close the isolation valve just after the T the problem does not occur - beyond the isolation valve this is where the air is collecting.

If I rotate the T to point downwards do you think this might help eliminate the air collecting?

I've attached a diagram of two ways I might be able to eliminate the air collection. What do you think? Will any work? View media item 31992
Cheers

 

[digdilem]

That air vent wasn't in the earlier pic!

If it's an auto vent, close the red cap fully and try again.

 

[picasso]

do you live a hard water area ?

 

[jonw]

digdilem, that latest drawing is a suggestion of what i might do next. The existing plumbing is the same as that but w/o the vent and with the T inverted possibly encouraging any air bubbles to collect in that piece of the pipework when the ensuite shower is running.

picasso, yes but installed a water softener about a year ago.

 

[picasso]

you might have scale build up on the bottom of your hot water cylinder, I have had this before where the pump is dragging air down the vent because the cold feed to the cylinder is too small or clogged with scale.

 

[Richard C]

The pump in my own property is a Salamander RHP which runs two showers & a bath faultlessly &, looking at you schematics, am a little surprised your getting problems, I cant really see any reason for it. Try fitting the vent or going to an Essex flange should cure it as they are far better at eliminating air (I always use them from preference). Only other thing I can think of is if the pump is of any age, the flow switch is acting up.

 

[jonw]

yes I think air is getting up the surrey flange and i think the reason it wasn't a problem before is that it was only driving one shower. Now that I 've added pipework there is a place for it to collect.

I intend to do the following;

1. rotate the T coupling to be horizontal or lower, add the vent, and try that for a couple of weeks
2. if that does't fix it i will change to an essex flange (may even do this as well to look after the pump).

Thanks for your help guys, I really appreciate all the suggestions. I will post back on here the outcome, probably in a couple of weeks time. Cheers