Shower Pump options

[robaxeman]

Hi,

I currently have a power shower located in an en-suite bathroom – approx 5 metres from the hot water tank. I want to replace the existing shower enclosure with a fully enclosed Shower Cabin, so I have to replace the power shower. My intention was to install a new dual-feed pump in the loft area above the en-suite to feed to the shower cabin below, making use of the existing hot/cold pipework. However, I read in the installation Instructions for a Salamander CT75 pump that it must be installed not more than 2 metres from the hot water tank.

Why is this? Would it be a problem if I installed 5 metres from the tank?

My alternative is to feed this shower off an existing pump which is installed above the hot water tank. I know this will be a problem if try to use both showers tat the same time – but that never happens now so should be OK??

Thanks for your help.

 

[seco services]

5m on 22mm pipe 2m on 15mm pipe.

 

[Richard C]

The pump should always be as near to the hws cylinder as possible & within the measurements stated. If you install a new pump, make sure you take time to read the instruction & understand how to design the pipe runs; I would only use 22mm not 15mm. A loft pump must be at least 600mm below the bottom of the cws tank; any up & over pipe work must also be below the cws tank & deliver at least 1 litre/min on both hot & cold with the pump switched off; up & over loops from the pump must be vented at the top with a nrv on the hot.

I assume you’ve checked the requirements of your new shower cabin; the multi jet, all singing & dancing affairs can demand a lot of high pressure water!

 

[robaxeman]

Thanks Richard C - but why must be within 2m, and what goes wrong if its further away?

 

[Richard C]

The reason for the pump being close to the tanks is that although they "pump" very well, the don’t suck very well. The longer the pipe runs to the pump, the more frictional resistance to flow, hence the difference in lengths between 15mm @ 2m & 22mm @ 5m = the larger the pipe, the less resistance to flow. The flow in the pipes will not be able to keep up with the demand from the pump & this leads to cavitaion, reduced pump pressure & could even damage the pump impellers . You could also experience problems with activation of the pump pressure switches.

 

[robaxeman]

Hi Richard C - that makes snese to me - thanks for the explanation - much appreciated.

It still makes me wonder though, why it is OK to have power shower, which also has a pump, located so far form the tank. Don;t these units also suffer from the same problems you describe?

Sorry to keep pestering for info! It just heps to understand why!

Cheers

 

[SUPERPLUMBER]

I believe that a 90 deg elbow adds a notional meter to the distance the water travels. i.e a 2 meter distance through a 90 deg elbow actually takes as long as 3m of straight pipe. you may be able to extend your pipe run from the hwsv using pulled bends as they offer very little resistance.

although id suggest you follow the manufacturers instructions

 

[Richard C]

It still makes me wonder though, why it is OK to have power shower, which also has a pump, located so far form the tank. Don;t these units also suffer from the same problems you describe? Sorry to keep pestering for info! It just heps to understand why!

Most electric showers have miniscule integral pumps & require minimum flow requirements compared to a purpose design power pump; think about the size of pump they can fit into that small housing & the size of your shower pump! Electric showers are great in certain circumstances but they are a bit of a con really as they rely on lots of small, high pressure water jets to give a false impression of a deluge of water. But getting a decent water flow can feel like someone’s drilling holes in your head & shoulders, only a high volume, high pressure pump will give you a comfortable deluge from an 8” or 10” rain head which is what most folks are after.

For the technical bit on pump design, I’ve never pulled an electric shower pump apart so I don’t know what type of impellers they use but all remote shower pumps I’ve had in bits use the same type of centrifugal, end impeller design; can’t remember the correct terminology! They are cheap to produce as they are not dependant on critical clearances between the impeller & the impeller housing but they are not tremendously efficient. If you’re moving fluids around, there are other types of impeller design that are far more efficient but take up much more space, more prone to damage & are far more expensive to produce; really not viable for domestic water application where the solution is just to mount the pump input as close to the water source as possible!

 

[robaxeman]

Well that also makes sense - thank you.

Actually our power shower does give a really good flow - it pumps both hot and cold water and is not an instantaneous electric shower, which I agree are usually rubbish.

So my options are to install a new pump close to the tank, or take a feed off my existing pump, making sure they are never used together.

Thanks for all your help - much obliged!

R.