The overflow of a small overhead pressure tank is being fed into this device. My concern is that the open vented device will let in smell and evaporated waste water. It might even cause a flood if there is a blockage somewhere. Am I scaring myself silly for no reason? Thanks.
Drainage for over head pressure tank overflow
- Thread starter DiyNutJob
- Start date
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1. The device is what is known as a tun dish. Its purpose is to let you know if there is water running through it (there shouldn't be) and to provide an air inlet to prevent an air lock / syphon forming.
2. Whether or not it will let smells in depends on where / how it is terminated:
3a. If into a soil stack, it could let smells in. Given that it is the vent for an expansion vessel, there should be no trap further in the system to prevent smells coming back.
3b. If it just vents to outside, no smells to come back.
4. If there is a blockage below the tun dish, water could come back and overflow the top of it. However, given that there should never be any water in it, this is unlikely but not 100% impossible.
5. To comment further on possible alternatives would need:
5a. A better description of what the "overhead pressure tank" is.
5b. Knowledge of where and how the white plastic pipe terminates.
2. Whether or not it will let smells in depends on where / how it is terminated:
3a. If into a soil stack, it could let smells in. Given that it is the vent for an expansion vessel, there should be no trap further in the system to prevent smells coming back.
3b. If it just vents to outside, no smells to come back.
4. If there is a blockage below the tun dish, water could come back and overflow the top of it. However, given that there should never be any water in it, this is unlikely but not 100% impossible.
5. To comment further on possible alternatives would need:
5a. A better description of what the "overhead pressure tank" is.
5b. Knowledge of where and how the white plastic pipe terminates.
The small overhead tank is used for providing pressure to the hot water tank sitting on the ground level. The the top of the immersion heater for the hot water tank is about the level of the water valves you see in the photo, or slightly higher.
The white pipe feeds in to a waste pipe that the basin waste feeds into. The two feeds are separate. The white pipe is closer to the point where waste waster is drained out of the flat below the concrete floor. The waste pipe is maybe half the diameter of the sewage pipe. These waste pipes are separate above ground. What is below, I have no way to tell.
See the white pipe here:
The white pipe feeds in to a waste pipe that the basin waste feeds into. The two feeds are separate. The white pipe is closer to the point where waste waster is drained out of the flat below the concrete floor. The waste pipe is maybe half the diameter of the sewage pipe. These waste pipes are separate above ground. What is below, I have no way to tell.
See the white pipe here:
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The tank will provide pressure for a hot water cylinder? Not sure what you mean by that? Do you mean it is a Pressure Vessel, i.e. an expansion vessel for an instantaneous HW heater and that is the temperature and pressure relief pipework, that's to cater for excess pressure/temperature if there is a fault condition in the heater?
If that is the case then it needs to follow certain regulations (Unvented HW) as far as pipe size and material is concerned. It needs to be able to withstand very hot water for a certain amount of time. Given that looks like 21.5mm overflow pipe I don't believe that will satisfy the requirements. It is also not trapped, so your concerns about smell could be warranted.
If that is the case then it needs to follow certain regulations (Unvented HW) as far as pipe size and material is concerned. It needs to be able to withstand very hot water for a certain amount of time. Given that looks like 21.5mm overflow pipe I don't believe that will satisfy the requirements. It is also not trapped, so your concerns about smell could be warranted.
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No. It's just a normal water tank with immersion heater. The property is all electric. The small plastic overhead tank is needed to provide water pressure to the hot taps in the kitchen sink, bathroom basins, and the bath. The cold taps are fed by the mains.
So the small tank (cistern) will be the cold supply for the HW cylinder? It's primary function is to supply the HW cylinder with cold water, it's height above the outlets is what supplies the pressure. It also needs to be large enough to ensure the hot water cylinder won't ever run dry. What size is the 'water tank' and what size is the HW cylinder?
If the cold is mains and the cold supply for the HW is from a cistern that is just above head height then the water supplies will be significantly unbalanced, that could cause havoc with mixer taps/showers etc working correctly.
If the cold is mains and the cold supply for the HW is from a cistern that is just above head height then the water supplies will be significantly unbalanced, that could cause havoc with mixer taps/showers etc working correctly.
Yes, your description is about right. The HW cylinder looks normal size. The cistern is fairly small, but is supplied by the mains. Unlikely the cistern would run low because it's being continuedly filled. It's a two bed flat. Unlikely all 4 hot taps would be on at the same time. Worst case would be 2 hot taps running at the same time. The hot flow rate wouldn't be great but passable.
There is a powered shower. The bath will have a mixer shower head. There was no mixer head before. I don't think it will be a problem for the bath to be used while a hot tap is used elsewhere.
I am no plumber, but I believe running the cold side will actually drag the hot side along in a mixer if both sides are open.
There is a powered shower. The bath will have a mixer shower head. There was no mixer head before. I don't think it will be a problem for the bath to be used while a hot tap is used elsewhere.
I am no plumber, but I believe running the cold side will actually drag the hot side along in a mixer if both sides are open.
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What capacity is the cold cistern and how many litres is the HW cylinder, it should be marked/labeled. What size of mains supply pipe runs to the cold cistern and what size of feed pipe runs from the cold cistern to the HW cylinder? It all really depends on the sizes, it doesn't matter if the cold water cistern is always filling, believe you me, the HW cylinder could empty the cold cistern faster than the cistern can fill, depending on the pipes sizes, capacities and flow rates. I have seen it happen a number of times with badly designed systems
When you say a powered shower, do you mean an electric shower or do you mean a power shower? They are quite different beasts.
I am a plumber and I can guarantee that the cold mains will not drag along the gravity hot, it does depend on pressure differentials but worst case is the cold mains pressure can stop the hot water running altogether.
I am not at the flat to know the tank sizes. The pipes feeding the taps are the smaller size, 15mm isn't it? The mains entering the flat is also valved with that size. While opening a single hot tap, the flow rate is quite acceptable.
I just know the powered shower works and it has a pull cord from the ceiling to turn on/off.
I am not a spray painter, but I know the flowing air drags the paint along. I imagine the same idea applies to the mains cold dragging the hot along. It doesn't bother me if I am wrong.
Anyway, should I delete the tundish? That white pipe is vented into the cistern anyway. Don't see why it would need another vent with the tundish. I think I got some idiot builders doing stupid things.
I just know the powered shower works and it has a pull cord from the ceiling to turn on/off.
I am not a spray painter, but I know the flowing air drags the paint along. I imagine the same idea applies to the mains cold dragging the hot along. It doesn't bother me if I am wrong.
Anyway, should I delete the tundish? That white pipe is vented into the cistern anyway. Don't see why it would need another vent with the tundish. I think I got some idiot builders doing stupid things.
I can see the reasoning for the tundish. If the regulation allows open venting of drain pipe air into living quarters then it's a bit f*cked up. In hot days, the vented air would carry moisture as well.
Anyone knows if this is compatible with my pipes? https://www.screwfix.com/p/mcalpine-tundish-19-23-x-19-23mm/5684v
Anyone knows if this is compatible with my pipes? https://www.screwfix.com/p/mcalpine-tundish-19-23-x-19-23mm/5684v
That's because the air runs over the top of a venturi/pipe, that then creates a vacuum in the tube that draws the liquid up and into the air flow, water works in a completely different way.
You do get specific venturi shower heads that do perform that function but that is very specific stuff and they're not easy to get these days I don't think.
I only mention it because I am very familiar with hot water that is fed from a cistern that is just above it and they have very poor pressure. I am also very aware of the problem that imbalanced water supplies cause (this hw set up coupled with mains cold water). If you all you are doing is supplying taps then you may get away with it but if it's is supplying mixer/monobloc taps then there may be. Again that's down to the difference in pressure between hot and cold, in London that might not actually be very much. Just don't want you to have all the work done then you end up with a very poorly performing system
The tundish is there to show when there is an issue with the cistern and when it overflows. It's a requirement when any overflow isn't externally visible. You can get one way sealed tundishes (Tun5 - CL) that perform the same function but a) are clear see thru and b) have a one way valve that seals up the pipe run to stop smells.
I know 1 mono block tap in the kitchen was fine as I lived in the flat in the past and didn't notice anything especially unusual. The system would have been adequately designed for low duty operation. It would not be suitable for anything beyond a couple plus a guest. We are not currently altering the plumbing and just installing new taps. I don't expect the mixer that comes with the bath to work all that great. But, cool or cold shower will be OK for the summer.
I have already asked the builder to change the tundish. If he wants labour for it, then I'll do it myself.
I have already asked the builder to change the tundish. If he wants labour for it, then I'll do it myself.
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