Low pressure hot water.

[dan83590]

I have just installed a new kitchen into a flat where they have a hot water cylinder on the same level as the kitchen. Before I started the hot water pressure was very low, it had low fitting budget type taps. Now I have installed I high swan necked mixer tap and the pressure of the hot water is pathetic.

I have double checked my work, its all fine.

Pressure at the bath is poor and pressure at the bathroom sink is fair.

How do I fix this problem? A pump or is there a simple way?

 

[Agile]

As a kitchen fitter, I would have expected that you would have know the difference between pressure and flow!

Also to have understood the basics of different hot water systems as they impinge on your work.

Tony

 

[dan83590]

I'm a carpenter not a plumber, but thanks for you help.

 

[dan83590]

So do none of you plumbers know how to permanantly repair this sort of situation with a retro fit solution?

 

[TicklyT]

What water pressure are your new taps intended for?
It usually tells you either on the box, or in the blurb in the instruction leaflet.

Incidentally, the position of the hot cylinder is usually irrelevant. It's the position of the cold tank feeding the hot cylinder that is significant.

 

[dan83590]

Thanks for your help.

I don't know for sure but the mixer supplied with the kit have the two small flexi hoses that screw into the bottom of the mixer so I am guessing that this is the wrong type of mixer??

(And before someone jumps in feet first, I don't design the kitchen I just fit what I am given)

The problem now is the very limited choice of low flow type mixers so I was hoping to offer a permanant solution.

 

[chapeau]

Best thing to do is increase the water pressure at the tap. Second best thing to do is increase the bore of the pipes going to the tap. Well I suppose the real best thing is to do both.

Increasing the pressure is probably easier. So

raise the feed tank (if in single floor flat not easy),

use the mains water pressure to drive the hot water (eg combi boiler or some unvented water tank system) so expensive. Or

put a pump on the hot water system which I am guessing is the easiest solution though not neccessarily as cheap as you might think. Probably known as a whole house pump. This will also affect any shower.........

Needs to be plumbed in and connected to electrics. If in a flat you will probably get a better solution if you get a negative head pump otherwise it might not kick in. If you only want to pump the hot then get a single impeller pump.

Plenty of terms to google but it can be done but needs to be done properly or else it will just annoy them even more.

I'm not a plumber either but I know this from experience (which is more than I can say for the 'plumber' who did some work on our house with an upstairs shower fed by a gravity system). At the end of the day it's just water flowing through pipes so the principles are straightforward, it's just applying them that confuses people, and it appears you know enough to do so.

 

[dan83590]

Okay thanks.

It is a single storey flat, the cold water tank that feeds the hot water tank can go no higher than ceiling level (2.4m ish), it is already as high as it can be placed.

Re-pipe with 22mm copper? How much would need re-piping, all of it to the tap then reduce to 15mm again, just a small section from the tank then reduce to 15mm or the whole lot in 22mm and then a 22mm tap fitting too?

Combi boiler is not feasible at the moment as the client has just spent their savings on this kitchen. I will mention this as a future solution though.

Pumped.. Something like this?

http://www.google.co.uk/products/ca...&sa=X&ei=S6efT7qbDoG48gP297l6&ved=0CHQQ8wIwBA

New specialised low flow/pressure mixers taps? Would these work?

http://www.screwfix.com/p/h-c-comme..._-H&C Commercial Lever Kitchen Sink Mixer Tap

http://www.bestbathrooms.com/produc...c&utm_campaign=25&pid=54419&cid=7547&affid=25

Thanks so far

Getting there!

 

[chapeau]

That's a positive pressure pump. Now it may well work, but a negative pressure pump should always work.

You can work out the maximum pressure at the hot tap...

Let's say the top of the water in the header tank is 2.2m above floor.
The outflow of your tap is 1.1m above the floor.
Difference is 1.1m.

1 bar = 10m water.

Therefore......

pressure at tap before you turn it on = 0.1 bar (give or take).

We have a greater head of water in our first floor bathroom and it's not enough to kick off the positive pressure pump our turkey "plumber" installed on the shower. We have to open a sink tap to get the thing to work.

 

[dan83590]

Those measurements would be roughly correct for this application too. Ceiling is 2.4m and I can just get my arm into the cold water tank. The worktop is set at 900mm from the floor (give or take as the floors are not level). So 2.2 minus 0.9 is 1.3. Does this mean 0.13bar at the tap? What are the sums you are doing?

The screwfix tap in the link above says a minimum of 0.1 bar required so this could do the job nicely.

 

[Agile]

Screwfix mean 0.1 Bar at the inlet to the tap!

Not 0.01 Bar when you have lost most of the pressure in the pipework.

There were/are special taps which are designed for low pressures but even these are unlikely to give a good flow.

A booster pump ( -ve head ) is likely to be the only proper solution.

Tony

 

[dan83590]

Nobody mentioned 0.01bar, or was that sarcasm?

So how do I work out what I have at the tap and what tap I need to offer?

There must be some simple sums to do?

 

[Agile]

The 0.01 Bar was my guess at the likely pressure at the tap inlet.

The makers details if available would enable you to work back to the inlet pressure if you jeasure the flow rate.

Calculations on pipework loss are quite complicated.

As I said a pump is the only practical solution.

Tony

 

[dan83590]

Okay.

Thank you for everyone's input. I'll let you know the outcome after speaking the the client.

 

[dan83590]

I found an online calculator for pressure drops and I have input the number and.

I worked out the head earlier to 0.13bar and the pressure drop has worked out at between 0.025 and 0.03 (we'll call it 0.03).

Leaving 0.1bar at the tap?

Does that sound feasible?

http://www.pressure-drop.com/Online-Calculator/index.html