Pressure Requirement for Water Fixtures

[EnOm]

Hi,
I have a question regarding the following:
I have a toilet at ground level that is supplied water from a small tank placed directly on top of the roof slab (It's part of an auxiliary building). The roof slab is +3m above the toilet's floor level. Disregarding friction losses, the maximum pressure that can be achieved is around 3m of head (~4.3 psi). According to what I have read, the minimum pressure for most water fixtures is about 8 psi.

So I am considering adding small pressure booster pump after the water tank to boost up the pressure.
I was also wondering what would happen if I went without the booster pump. Will the water pressure still be acceptable, even if barely? I'm trying to keep costs down.

Thank you

Best Regards

 

[MikeHalloran]

Try it without the pump first.
It should work okay, if it's a common toilet with gravity operated valves.


If it's a pressure flush toilet, it probably won't work on that little pressure.

<tangent>
Toilets with the Sloan pressure flush mechanism are the only low-volume toilets I've seen that actually work.
</tangent>



Mike Halloran
Pembroke Pines, FL, USA

 

[EnOm]

MikeHalloran,
Thank you for the reply. I can't try it because the building is in design phase, nothing has been built yet. This is not something I usually do so I don't really know that much about these things. What if there was a standard shower (mixer + flexible hose to the shower head) in there as well, would the shower function adequately without the boosting?

Regards

 

[MikeHalloran]

So, the shower would have ~1.5m of head.
People have been showering under perforated bags just overhead for a long time.

A standard showerhead might need to have the 'water saving' restrictor removed in order to work well.
That might be a legal problem, depending on your jurisdiction.



Mike Halloran
Pembroke Pines, FL, USA

 

[PEDARRIN2]

If the building is in the US, the plumbing codes typically have minimum pressure requirements for plumbing fixtures.

For the IPC, a water closet requires a flowing pressure of 20-35 psig, depending on if it is tank or flush valve. A shower requires 8-20 psig flowing pressure.

If some type of backflow preventer is required, that will reduce available pressure.

I would provide a pump.

 

[EnOm]

MikeHalloran,
Thank you for the the useful input. I'm sure I'll find it useful when making the final arrangement.
Regards

PEDARRIN2,
Thank you for the reply. The building is not in the U.S. It is in Qatar. I'm not really sure what the local code is, my main concern at this point is for the water supply to function properly to avoid complaints from the client. The code usually conforms with sound engineering so I guess if I satisfy one the other should follow suite.
By 20-35 psi flowing pressure you mean after all the head losses right? I think there is quite a significant difference between 20-35 psi after (valve+flexible connection) and before them.

Regards

 

[MikeHalloran]

Sorry, I thought you were talking about your own e.g. mountain cabin.

Specify the pump.


Mike Halloran
Pembroke Pines, FL, USA

 

[EnOm]

MikeHalloran,
I was not being sarcastic .
I'll need pump that can give 0.3 L/S @ 33m Head (~47psi). Grundgos CME 1-4 seems alright. However, I'm not specifying the exact pump on the drawing this is just for my reference only.

Regards

 

[PEDARRIN2]

Flow pressure is the pressure after all the static and friction losses are taken out.

If the water closet is a tank type, you are likely ok (it might take a bit longer to fill the tank).

The shower and lavatory would likely not have a lot of pressure behind it, but I have seen worse.

I would still recommend a pump (constant speed with a bladder tank if cost is a concern), merely to make sure the flow out of the shower/lavatory is not a trickle.

I would design it for 8 psig after all the pipe friction losses have been accounted for.

 

[Drazen]

i am surprised to hear about so high requirements at draw off points, from reference avaiable, bs requirements specify 17 kPa for shower (highest requirement), that should be 2.5 psi. din asks for 100 kPa for some shower heads, which i always considered quite conservative.

 

[PEDARRIN2]

A shower will operate at less pressure but the results may be less than satisfactory to the user/client.

The showering experience can drive the design.

I had a college dorm project where the pressure at the shower head was measured at 50 psig (which is 30 psig higher than required by code). I designed it for 40 psig. I specified low flow shower heads (1.5 gpm)for water conservation. The college mandated the low flow heads.

There were a lot of complaints about the showers from female occupants due to the time it took to rinse out the shampoo in their hair.

Needless to say, the college is investigating replacing the shower heads with higher flow versions.

 

[EnOm]

PEDARRIN2,
Thank you for your response. The information you provid gives me some useful insight. You are right, it all depends on the level of comfort expected by the client.