Which Pump? (Minimal Head)

[barki]

Hi

I'm replacing two upstairs bathrooms at the same time. They share a common wall (stud & p/board) which I am expanding slightly to accommodate routing of waste & water pipes. I've now stripped out both rooms with the exception of the shower cubicle.

For interest, but not vital to this question, there is a diagram below.

Anyway, the existing set up has a Salamander CT50 Twin pump mounted directly above the shower on the p/board ceiling inside the attic. It is 460mm below the cold water tank, which is raised on a plinth above the ceiling joists. The pump works reasonably well but it noisy as you'd expect. Both hot & cold feeds to the pump are plumbed in 15mm copper.

I intend to run two showers from a single pump on the new system. Both have large heads. Both will be on the upper floor, with outlets perhaps 600-800mm below the cold water tank.

I realise that, ideally, I'd place the new pump either on the floor in the airing cupboard, or under the bath. While I feel I can manage the plumbing to either location (although space is very limited in both cases) , I don't want to have to employ a spark to re-wire to the new location if possible (the existing pump is wired, via a fuse, to the upstairs lighting ring). Hence, I think it would be easiest to replace the existing pump in it's current position but I have some questions;


-Should I pay the extra for a negative head pump? Most of the manufacturers seem to state that a 600mm drop from the tank is required for a positive head pump, I only have 460mm. Also, both shower heads will be below the pump height.

- Should I bother re-plumbing with 22mm pipe from the cold tank & h/w tank, or will a decent pump still give reasonable pressure through 15mm to power both showers. (I think both running at the same time will be very rare....the h/w cylinder isn't that big anyway!)

- Do you have any pump reccomendations,....I'm looking at the Stuart Turner Monsoon Twin 3.0 bar, but its pricey!! Would 2.0 bar cut it?

- Are the 'anti vibration pads' I see for sale online any good, price at about £25! I'd hope an expensive pump will be quieter...


Really grateful for anyone's advice or opinion on anything above

Cheers!

Tom


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[Newboy]

(the existing pump is wired, via a fuse, to the upstairs lighting ring).

Not a good idea as the pump may be drawing close to the maximum current for a lighting circuit

-Should I pay the extra for a negative head pump? Most of the manufacturers seem to state that a 600mm drop from the tank is required for a positive head pump, I only have 460mm. Also, both shower heads will be below the pump height.

If the manufacturer gives a recommendation then it's a good idea to follow it - if the pump doesn't work then you're stuffed!

- Should I bother re-plumbing with 22mm pipe from the cold tank & h/w tank, or will a decent pump still give reasonable pressure through 15mm to power both showers. (I think both running at the same time will be very rare....the h/w cylinder isn't that big anyway!)

Depends on the pump specifications - most of the higher capacity pumps require 22mm

- Do you have any pump reccomendations,....I'm looking at the Stuart Turner Monsoon Twin 3.0 bar, but its pricey!! Would 2.0 bar cut it?

Stuart turner are one of the better manufacturers - you need to look at flow rates rather than just pressure

- Are the 'anti vibration pads' I see for sale online any good, price at about £25! I'd hope an expensive pump will be quieter...

waste of time you can achieve the same thing by acoustically isolating the pump on rubber blocks



It's worth checking the flow rates for the shower heads and pumps - you'd be surprised how quickly you can empty a hot water cylinder

 

[ALCPlumbing]

It's the height between the outlets and cold water tank that is important. You've said they are 600-800mm. This is fine for a positive head pump. As long as water will run from the outlet unaided then it will be able to trigger the pump. You only need a negative head pump to compensate when that isn't the case. It will store a small volume of pressurised water which when the outlet is opened will trigger the flow switch to start the pump. They need maintaining in the form of pressurising the vessel. You don't need it so just get positive. It's cheaper as well.
If you want one pump to do both showers I would upgrade to a Stuart Turner monsoon pump, the come in a range of pressures, with 22mm supplies as this will cope with the demand of two showers at once.

 

[Newboy]

It will store a small volume of pressurised water .

Really? - that's a first!

 

[barki]

Hi,

Thanks thats been really helpful much appreciated! I notice that the pump power rating will be going up a bit, from 480w to 650w....I guess i'll need to calculate the total load on the circuit now (but shouldnt the breaker be rated at 1.5x the total load and be able to cope?)?

Cheers again, Tom

 

[Newboy]

The breaker's job is protect the circuit - if the load is higher than the circuit is rated for then you shouldn't up the breaker rating (unless you want to risk damage to the circuit/fire). It's worth remembering that the start-up current from the pump will exceed it's stated consumption (only briefly) & may be enough to trip the protective device.