Hi - I live in a townhouse (3 storeys) whihc has direct main feed cold to all outlets and low pressure hot. I am fitting a new shower down stairs - it will be feed from main cold and low pressure hot. The hot has about 6 meters of head. Will a normal 'mixer' shower work or should I go for Venturi style? Do anyone have experience of these venturi showers?
Shower - Mains cold, low pressure hot
- Thread starter james2006
- Start date
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it's unlikely it'll work as you want.
i'm in a similar position and have done a fair bit of reading,
so i may be wrong on some points but to summise..
6m of head equates to roughly 0.6bar best case scenario
mains pressure is ?? (assuming 4 bar..)
would mean the mains is nearly 8 times more pressurised than the hot water,
worst case scenario, the mains cold will force its way up the hot pipe,
out the expansion pipe above the tank and you'll have an overflowing cold water cistern in the loft.
best case, you'll have a temperamental mixer that will be on a razors edge between hot and cold.
The simplest solution you'll get is to take a new cold feed from your cold water cistern and use this along side the hot,
this means the two would be at the same pressure (as they both have the same head)
My cold water tank isn't big enough to do this, so i'm doing it a different way to cure my problem, using a few things.
1) a PRV (pressure reducing valve) on the incoming mains set to about 3 bar, limits incoming pressure so the differental between hot and cold isn't too great.
2) 2 PEV's (pressure equalising valve), one for my basin mixer and one for the feed to the shower, which should bring the cold pressure down to match the hot, it also includes check valves / non return valves to stop the overflowing cold water cistern, these need to be cleaned out periodically so isolation before the PEV as well.
3) a thermostatic shower mixer, just because i don't like being shocked by cold water
i'm in a similar position and have done a fair bit of reading,
so i may be wrong on some points but to summise..
6m of head equates to roughly 0.6bar best case scenario
mains pressure is ?? (assuming 4 bar..)
would mean the mains is nearly 8 times more pressurised than the hot water,
worst case scenario, the mains cold will force its way up the hot pipe,
out the expansion pipe above the tank and you'll have an overflowing cold water cistern in the loft.
best case, you'll have a temperamental mixer that will be on a razors edge between hot and cold.
The simplest solution you'll get is to take a new cold feed from your cold water cistern and use this along side the hot,
this means the two would be at the same pressure (as they both have the same head)
My cold water tank isn't big enough to do this, so i'm doing it a different way to cure my problem, using a few things.
1) a PRV (pressure reducing valve) on the incoming mains set to about 3 bar, limits incoming pressure so the differental between hot and cold isn't too great.
2) 2 PEV's (pressure equalising valve), one for my basin mixer and one for the feed to the shower, which should bring the cold pressure down to match the hot, it also includes check valves / non return valves to stop the overflowing cold water cistern, these need to be cleaned out periodically so isolation before the PEV as well.
3) a thermostatic shower mixer, just because i don't like being shocked by cold water
Thanks for reply - mains is at around 3 bar - so pressure difference will be an issue. Running a new pipe from the loft tank is going to be a difficult job as tank is effectively in floor 4 and bathroom on first floor.
Did you look at a venturi shower at all? Do you know anything about this?
Also could I get a PRV to reduce main pressure to 0.6 bar?
Did you look at a venturi shower at all? Do you know anything about this?
Also could I get a PRV to reduce main pressure to 0.6 bar?
I think PRV's normally only come down to 1 or 1.5 bar,
still not enough to give you a balanced supply for a normal mixer
**edit, why not just use a PEV in your case, most can cope with a 10:1 difference ??? **
but that would might be low enough for a low pressure thermostatic mixer,
the ones i've been looking at can cope with a 5:1 pressure difference
PRV's also need cleaning out periodically, most come with a strainer for the incoming supply and it'll need clearing out if it becomes clogged.
i'd only fit that to the shower if you want to go that route, as if you fit it to the mains, you'll reduce the feed to all the taps / cisterns down to that.
i did have a look at venturi, but the choice is rather limited, and they have a specific operating range of flow and pressures, need at least a 22mm hot feed and preferably a 15mm cold feed,
and moving the shower head up and down causes the temperature to fluctuate (as you alter the head resistance and thus the venturi effect changes).
nice idea in principle but it's not something i fancy.
still not enough to give you a balanced supply for a normal mixer
**edit, why not just use a PEV in your case, most can cope with a 10:1 difference ??? **
but that would might be low enough for a low pressure thermostatic mixer,
the ones i've been looking at can cope with a 5:1 pressure difference
PRV's also need cleaning out periodically, most come with a strainer for the incoming supply and it'll need clearing out if it becomes clogged.
i'd only fit that to the shower if you want to go that route, as if you fit it to the mains, you'll reduce the feed to all the taps / cisterns down to that.
i did have a look at venturi, but the choice is rather limited, and they have a specific operating range of flow and pressures, need at least a 22mm hot feed and preferably a 15mm cold feed,
and moving the shower head up and down causes the temperature to fluctuate (as you alter the head resistance and thus the venturi effect changes).
nice idea in principle but it's not something i fancy.
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Thanks - I just had a look at PEV and found this one - looks like would do the trick.
http://www.plumbworld.co.uk/pressur...gleBase&utm_medium=GB&utm_campaign=GoogleBase
However, the PEV will reduce the shower to pressure of hot (lets say 0.6 bar) - I assume this will work for thermostatic shower mixer and give ok flow rate?
Cheers
http://www.plumbworld.co.uk/pressur...gleBase&utm_medium=GB&utm_campaign=GoogleBase
However, the PEV will reduce the shower to pressure of hot (lets say 0.6 bar) - I assume this will work for thermostatic shower mixer and give ok flow rate?
Cheers
it will come down to which mixer you get,
have a look at the specs, they normally show a flow rate @ x bar
it isn't a guarantee as most figures are without a shower head.
the ones i'm looking at generally show about 7 L/min @ 0.2 bar
have a look at the specs, they normally show a flow rate @ x bar
it isn't a guarantee as most figures are without a shower head.
the ones i'm looking at generally show about 7 L/min @ 0.2 bar
PRVs are available that go down to half a bar, but they are threaded.
Reliance and Altecnic both do one.
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