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Water pressure planning in dental clinic

I have a dental clinic at first floor in delhi under construction.

Due to few reasons we are installing a water tank (300-500 lt) inside the clinic at 11 feet height. While, the chairs would be 14 feet and 30 feet (floor measurement) away from water tank.

I'm afraid, that due to small diameter of dental chair water tubing, the pressure at watercup filler and spitoon in dental chair would be too less.

I've gone through your answers regarding this problem related questions like hydro pneumatic system, or increasing the diameter of outlet pipe, or increasing the level of overflow pipe,but can this be applied considering the narrow diameter of dental chair tubing (2-3mm)


Dr. Nitin Rohatgi



1. Dr. Rohatgi, Your question is

Dr. Rohatgi,

Your question is in the domain of fluid mechanics, and not really about “water issues” in the colloquial sense. While you have voiced concern about the pressure at the water cup filler being too less, actually what you mean is – the flow rate will be too less. Pressure at the outlet is always atmospheric pressure, and any residual pressure head is converted to kinetic energy - like the high velocity jet you get when you put a nozzle at the end of a tube to wash your car (which you shouldn't. Wipe it with a wet cloth).

The outlet in a dentist chair is typically at 3 to 4 ft from the floor. You have stated that the tank is being installed at 11 ft height. If it means that the bottom of the tank will be at 11 ft from the floor, then that gives a hydraulic head of minimum 8 to 7 ft + the height of water in the tank. I have (unfortunately) sat many times in the dentist chair and am aware of the flow rate required. I do not think there will be any problem. Consider this - the roof top tanks in a bunglow are about 10 ft above the floor, and the shower head is 7 ft above the floor. So the hydraulic head is 3 ft + the height of water in the tank. It is sufficient for a good flow with a ½ inch GI pipe.

I hope you do not use that thin tube all the way from the tank. Use a standard ½ inch pipe upto the chair. Preferably use what is known as UPVC or CPVC, instead of GI (it offers less friction), minimize the bends and valves in this pipe, and you will get sufficient flow rate.

 Chetan Pandit

2. Water pressure planning in dental clinic

Dear Nithin,


Could you please share some more information that will help me to respond to your query?

1. What is the flow anticipated at the spitoon?

2. What is the pressure anticipated at the spitoon?

3. Is the tank 11 fleet high from the floor of the clinic? If so the net head available will be around 7-8 feet considering the height of the chair.




Mohanasundar Radhakrishnan

Project Officer - Arghyam

3. Water pressure planning in dental clinic

Dear Dr. Nitin Rohatgi,

What you have missed out is what is your water pressure requirements at the watercup filler and spitoon in dental chair.

Anyway, if you want to have a higher pressure, you will have to install a water pressure booster pump which is very small, the size of a water meter and could be installed at the outlet of the water tank itself.

These are online booster pumps manufactured by GRUNDFOS  a 0.5 hp pump will develope  up to 1.5 kg pressure at the outlet points. and it is switched on and off when the tap is turned on and turned off. The narrow tubing will not make any difference where the pressure is concerned. You may be able to set the maximum and minimum pressure you require on the pressure regulator switch


Anil Lalwani

4. Further to my reply

Further to my reply yesterday, who so ever advised you to increase the height of overflow pipe to increase the hydraulic head (pressure, as most call it) needs to read some elementary fluid mechanics. If it was that simple, then for colony water supply instead of constructing over head tanks 60 or so feet high, we would construct them at ground level  - much cheaper - and just attach 60’ tall overflow pipes to get adequate “pressure” in the taps.

Overhead tanks are not sealed pressure vessels. The free water surface in the tank is at atmospheric pressure, and the water level in the overflow pipe is also at the same level, and pressure. However, even if a tank is constructed as a sealed vessel and filled under pressure, the water level in the tall overflow pipe would be higher, but that would last only for a short while. The small quantity of water in the pipe will be the first to get used, and thereafter the water level in the pipe will again be the same as in the tank.

Chetan Pandit

5. thanks a lot

dear all...

i really thank you all for your genuine concern and excellent advice...

to clarify few facts(according to use) for Mr. M. Radhakrishnan:

1. flow anticipated - at cup filler-150ml glass to be filled in 5-6sec

                          - at spitoon- sufficient to wash out saliva/small food debris

2. the floor of the tank would be 9 feet above clinic floor and the height of the spitoon/cup filler would be around 3/3.5 feet above floor.


Dr Nitin Rohatgi

6. Water pressure planning in dental clinic- in continuation

Dear Dr Rohatgi,

Just thinking about your water pressure problems.

It just occured to me, that you would probably lay the pipes from the overhead tank, (without any air release system), all the way to the ground and then horizontally to the spitoon and then to the outlet at about 3 ft above  the ground.

With this kind of pipeline arrangement, you will get problems due to airlocking in the pipe, this would occur everytime the level of water in the tank is low, and will be more if the overhead tank needs to be emptied for cleaning or happens to get emptiesd due to use.

Even though the idea of a pressure booster pump is a bit far fetched, but would be ideal to ensure that a constant pressure is achieved everytime the tap is turned on.


Anil Lalwani

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