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### Author Topic: How do I get enough water pressure in my plumbing?  (Read 2613 times)

#### Thebox

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##### How do I get enough water pressure in my plumbing?
« on: 21/10/2015 14:12:04 »
Hello I need some science help with some plumbing I have to do in my bathroom. The original toilet was not filling and was an old toilet so have replaced the toilet which is still not filling. The system is a gravity based feed from a header tank that sits above the toilet height and the force of gravity allows the water to flow down and then upwards into the toilet system by gravity pressure.
However the system is short of pressure, so the system is failing, a simple fix would be to raise the tank into my loft creating more potential energy and force and pressure of the water, however I have also fixed in place some mixer taps with a shower head, however the obvious is that the pressure is not enough to work the shower head when it is raised above the hot water tank height.

I have an idea to put a tee junction in from the main water supply and pressure, and connect this to the cold of the mixer tap which is gravity fed, to create an invert flow and pressure. Will this work?

a-main feed
b- gravity fed
c-invert flow

In future, please phrase topics as a question - Mod
« Last Edit: 21/10/2015 20:31:14 by evan_au »

#### Colin2B

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##### Re: A gravitational and pressure problem -plumbing related
« Reply #1 on: 21/10/2015 14:42:13 »
Can I check, do you have a current problem with the shower mixer or just with toilet? Has this always been a problem? Just wondering if some pipe work is clogging up?
A few points to consider.
You can feed the toilet cistern from a mains pipe but you need to check you have a ball/control valve which will handle the extra pressure, sometimes you can get a different valve unit.
The shower head will work if it is above the level of the hot water tank because the HW tank is fed from the loft tank and so is at same pressure. You might have a problem if you feed cold from mains to the shower because some mixers are not designed to take differential pressure and to be honest you would still have a pressure problem on the hot feed if it is a tank height problem.
If you teed into the cold main as in your diagram you would need to isolate mains and tank supplies to prevent drawback into the drinking water. So either a no return valve or separate the pipes ie no interconnection.
Personally my first look would be at why you have poor tank pressure. What is the height of the header tank above the toilet inlet? Are you sure the pipes are not clogged?

#### Thebox

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##### Re: A gravitational and pressure problem -plumbing related
« Reply #2 on: 21/10/2015 14:52:14 »
Can I check, do you have a current problem with the shower mixer or just with toilet? Has this always been a problem? Just wondering if some pipe work is clogging up?
A few points to consider.
You can feed the toilet cistern from a mains pipe but you need to check you have a ball/control valve which will handle the extra pressure, sometimes you can get a different valve unit.
The shower head will work if it is above the level of the hot water tank because the HW tank is fed from the loft tank and so is at same pressure. You might have a problem if you feed cold from mains to the shower because some mixers are not designed to take differential pressure and to be honest you would still have a pressure problem on the hot feed if it is a tank height problem.
If you teed into the cold main as in your diagram you would need to isolate mains and tank supplies to prevent drawback into the drinking water. So either a no return valve or separate the pipes ie no interconnection.
Personally my first look would be at why you have poor tank pressure. What is the height of the header tank above the toilet inlet? Are you sure the pipes are not clogged?

Thank you Colin, the pipes are definitely not clogged in any way, if if disconnect the water feed from the cistern tank, water comes out, there is just not enough pressure to force the water upwards into the cistern, the mixer taps are new, both hot and cold water in the bathroom are gravity fed, to improve my hot water pressure I was going to turn up the temperature and then hopefully the cold water flow will take the hot water with it up the shower pipe.

The drinking water is on the mains, so any mains water would be going back into mains water of the tank, estimate the tank is about 3ft above the cistern.

#### Colin2B

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##### Re: A gravitational and pressure problem -plumbing related
« Reply #3 on: 21/10/2015 15:12:20 »
, to improve my hot water pressure I was going to turn up the temperature and then hopefully the cold water flow will take the hot water with it up the shower pipe.
That won't work as you would need a lot of flow to create sufficient draw.

The drinking water is on the mains, so any mains water would be going back into mains water of the tank
But it would be going via the outlet pipe of the header tank, so the tank would fill and overflow as the water is bypassing the ball valve!.

You need to ask your plumbing supplier about the tank height, is it enough for the fitting supplied. It doesn't sound high enough for me, but it must have worked at some stage?

Certainly the header tank needs to be higher than the top of the shower head and 3ft above the shower head should be ok for that. Sounds as though you need to raise the tank for the shower, or fit a pump.

#### Thebox

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##### Re: A gravitational and pressure problem -plumbing related
« Reply #4 on: 21/10/2015 15:47:19 »
, to improve my hot water pressure I was going to turn up the temperature and then hopefully the cold water flow will take the hot water with it up the shower pipe.
That won't work as you would need a lot of flow to create sufficient draw.

The drinking water is on the mains, so any mains water would be going back into mains water of the tank
But it would be going via the outlet pipe of the header tank, so the tank would fill and overflow as the water is bypassing the ball valve!.

You need to ask your plumbing supplier about the tank height, is it enough for the fitting supplied. It doesn't sound high enough for me, but it must have worked at some stage?

Certainly the header tank needs to be higher than the top of the shower head and 3ft above the shower head should be ok for that. Sounds as though you need to raise the tank for the shower, or fit a pump.

Yes I understand what you are saying about the tank filling up from the bottom from the invert flow pressure being greater than the gravity pressure of the tank, and understand what you are saying about creating enough sufficient draw. I did consider a pump or raising the tank, however the main tank pipe gage is old and they do not do that any more, where as some of the 15 mm outlets I can get the parts for.

I have also worked out that if I raised the hot water tank approx 1.5ft the water would flow, so some how I need to produce 1.5ft worth of pressure of the hot flow, I was hoping more heat would do this.

For the cheap option I either forget it or need to try it this way, I have a pressure valve so if I adjust the pressure accordingly of the main flow, do you think I will find a balance of force that will stop the tank backfilling?

#### Colin2B

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##### Re: A gravitational and pressure problem -plumbing related
« Reply #5 on: 21/10/2015 16:02:57 »
.., so some how I need to produce 1.5ft worth of pressure of the hot flow,
If you raise the header tank this will also provide more hot pressure as the hot tank is fed and pressurised from the header tank.

#### Thebox

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##### Re: A gravitational and pressure problem -plumbing related
« Reply #6 on: 21/10/2015 16:12:21 »
.., so some how I need to produce 1.5ft worth of pressure of the hot flow,
If you raise the header tank this will also provide more hot pressure as the hot tank is fed and pressurised from the header tank.

Thank you , that would be the easy option if the pipe gage I could still buy, I would have to replace all the pipes in the house more or less if I move the header tank.
I wish I knew what the mass of the water in the header tank was, or the litres it held, I could work out the force it was applying then compared to  the mains pressure to calculate if it will work.
The header tank has an over flow system so hopefully if I try it i wont over fill the tank and flood.
Do you think my idea is worth trying or is it destined to failure?

I am sure the cold water will come out of the shower head being put on the mains but I am not sure about the sufficient draw now you mention it, I am sort of trying to syphon the hot  up the shower pipe

#### Colin2B

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##### Re: A gravitational and pressure problem -plumbing related
« Reply #7 on: 21/10/2015 19:25:58 »
You should be able to buy capillary adapors for joining 15mm to old pipe. But if you use compression fittings 15 will fit old 1/2 in, but to connect 22mm to 3/4 you will need to ask for an oversize olive.

You don't need to know mass of water to work out pressure. Just distance between bottom of tank and tap in meters. 10m=1bar so 2m = 0.2bar etc. compare this with tap spec.

You won't be able to siphon hot water up the shower, not good physics

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#### Thebox

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##### Re: A gravitational and pressure problem -plumbing related
« Reply #8 on: 21/10/2015 21:02:24 »
You should be able to buy capillary adapors for joining 15mm to old pipe. But if you use compression fittings 15 will fit old 1/2 in, but to connect 22mm to 3/4 you will need to ask for an oversize olive.

You don't need to know mass of water to work out pressure. Just distance between bottom of tank and tap in meters. 10m=1bar so 2m = 0.2bar etc. compare this with tap spec.

You won't be able to siphon hot water up the shower, not good physics

Thank you Colin, you sure do know the science of plumbing.  I decided not to attempt the shower at this stage but successfully changed the toilet to the mains rather than gravity fed, fixing the toilet fill.  I think I will go down the path of a pump for the hot water feed to the shower, great advice thanks again.

#### The Naked Scientists Forum

##### Re: A gravitational and pressure problem -plumbing related
« Reply #8 on: 21/10/2015 21:02:24 »