Dear Hans,

You have asked a good questions

in my opinion , we have two solutions:

at the industry level, you can use Constant Pressure Pumps like this demontration https://www.youtube.com/watch?v=GtC_Qf1Zd4Q.

in the laboratory you can use your own tank with a standard pump

Best regards 

Dear Tarik,

Thanks for your suggestions. The provided background information was expanded based on your feedback. We have tried some pumps without success. Will have a look at the pumps you suggested.

Our current hypothesis to reduce the feed pressure a bit (from e.g.) 3.5 to 3.0 bar using a pressure reducer. This may reduce the pressure variation. Possibly this could be combined with a pressure dampener. If you have suggestions, please let me know.

Best regards,

Hans

Dear Azizul,

Thanks. can you provide information on a constant pressure pump type/brand without pulsations?  I had contact with several (major) pump suppliers and they could not deliver such a pump or when a pump was tested it showed to give pressure/flow pulses,

Best regards, Hans  

Dear Hans,

What is your water source? Does it come from a municipal water supply or is it from a well?

George

Dear George,

It is from a municipal water supply. The drinking water is produced at a large treatment facility (annual drinking water production was 40 x 10^6 m3 per year) and transported by the distribution network. Surface water was treated at this location by coagulation, flocculation and sedimentation followed by ozonation, dual medium filtration, and granular active carbon filtration. Final disinfection (0.1 mg/L chlorine dioxide) was applied at the inlet of a large storage reservoir where the water was collected before distribution. The concentration of chlorine dioxide in the reservoir effluent was below the minimum detection limit (

Dear Hans,

I see.  My reason for asking is that it is quite common in the US to use a pressurization tank on private wells to ensure that there is adequate pressure to distribute water throughout a building. These tend to act as a buffer and to help maintain steady pressure on the system. I believe that similar solutions are used in combination with supplementary pumps in larger buildings to maintain steady pressure.

George

Dear George, I will look into the suggestion you made and let you know. Thanks. Hans

Dear Hans: A maximum variation of 0.2/3.5 = 6% in pressure, in fact does not look much for a pump (independently if it is driven by a motor with constant or variable speed) and will be expected to cause a maximum variation of only about 3% in water flow rate in a tap (discharging in atmosphere) for a constant geometry (the observed maximum differences could reach magnitudes of only 3 and 6 liters/hour in 100L/h and 200 L/h, respectively?). At what minimum pressure can you perform your experiences? Assuming that the problem is the pressure variation, and given that the flow that you mention is very little, it would be possible an open regularization tank upstream at constant level (or a closed tank with air under pressure, if it would be required a very high level) that could be easily regulated at a constant level (and constant air pressure, if necessary)? Does not the municipal water supply system have a regularization reservoir after the treatment station that you mention and that supplies (by gravity) the area of your building?

Dear António,

Thanks for the detailed feedback. We think a minimum feed water pressure of about 1.8 bar is needed for our studies. So an open reservoir would not be suitable for such pressure. Will have a look at the closed tank option you mentioned. I am not sure whether the municipal water supply has a regulation reservoir (assume not). However,  we noticed pressure/water flow variations in our monitor system that seem to be linked to the feed water pressure variation. We are now testing a pressure variation dampener and a pressure reducer.

Best regards, Hans

Dear Hans

What is the distance of the pipe line (branch) that come from the main line (branch) of the water  distribution system operating to your lab, and one more important thing is that ,  is there any connection between this branch pipe and other user before coming to your lab? if so the main  fluctuation would be,  because of that, you should use the line which doesn't  have any change in diameter and doesn't have any other user before coming to your lab otherwise you will have this fluctuation anyway.

Dear Yusef,

Our set-up: The pipe line distance and diameter in our building is not known to our research set-up. Assume it is about 100 meter. The last part of the pipe has 2 cm internal diameter, which is quite sufficient for our maximum water use.

Building: the water pipe in our building has many other connections as well (taps, toilets, set-ups, autoclaves,), possible causing/contributing to the experienced pressure variations.

It would be nice to have a direct connection between a large water pipe (prior to our building) and our set-up. Maybe it is an idea to test our equipment at a location with water supply directly from a large diameter pipe in the network. Then we know whether the building piping and water use is responsible.

Best regards, Hans

Good, you can test it at another location.

Good, you can test it at another location.

Good luck .

Siphoning shall give the constant pressure flowrate. Use a elevated intermediate vessel for siphoning, where you will feed tap water. Due to elevation of intermediate vessel you will get a constant potential difference, which will give constant pressure flowrate. Also, make sure inlet and outlet pipe of the intermediate vessel should be of same diameter.

Dear Sameer,

Thanks for your suggestion.

We pursue to have a constant flow rate without pulsations through a monitor in which biofilm formation will occur with time. This biofilm formation will cause an increase in hydraulic frictional resistance (pressure drop) with time. So we need to maintain a constant pulse free water supply (e.g. 16 L/h) while the resistance over the monitor will increase with time.

A constant feed pressure using e.g. an overflow vessel will cause in our monitor system a reduction of of flow rate with the increase of biofilm resistance with time. We like to keep the flow constant and study the biofilm accumulation.

Our current testing involves in the feed water pipe the installation of a pressure dampener and two pressure reducers in series. These systems are installed before the water is fed to the monitors. After the monitor is a back pressure valve installed.

Best regards, Hans

Dear Sameer,

Thanks. Based on your feedback the introducing text of the question has been adapted.

Best regards, Hans

Dear Hans I guess you have to create a flow through tank from your primary water supply with e.g 10 L volume, overflow directed to sewage I assume you could have a flow of e.g. 30L/h. From that buffer tank you can pump with any pump you like your constant flow. as long as you pump delivers the constant flow. - I assume any technically suiting pump (cilinders maybe better than rotators).

Dear Kai,

Thanks for the suggestion. We are looking at a very constant water flow at a very short time scale (0.01 s) while doing research over several days. Fully agree that (multi)cilinder pumps are better than rotor tube pumps.

Best regards, Hans  

Dear all,

Based on your feedback and a survey progress was made. We are able to achieve a constant pulse free feed water flow (16.00 kg/h +/- 0.1%) combined with a relative stable dosage of chemicals to the same water stream (100 g/h +/- 0.6%). This was achieved by using a combination of pressure dampener and two pressure reducers in series in the feed tap water (no residual disinfectant) and using regulated coriolis meters for the flow and dosage. The first exploratory long-term study on biofilm formation showed good results.

Best regards, Hans