To what extent does unstable water pressure affect the accuracy of turbine flowmeters?
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Dear seniors, I have built a device for a client aimed at measuring both the instantaneous and cumulative flow rate of water. However, the client is not satisfied with the current measurement results and wants improvements. I identified several factors that affect accuracy. But there is one factor I’m not sure about, namely: the water source at the inlet side is provided by the customer; we just need to connect the equipment’s pipes to it. The problem is that the water pressure at the customer’s location is very unstable, fluctuating frequently within the range of 0.1 MPA. What I want to know is whether such unstable water pressure will affect the measurement results of my flow meter, and to what extent? I earnestly ask for your guidance, esteemed seniors!
1. What is the relationship between water pressure fluctuations and the pulse counting of the turbine speed? The water flow drives the turbine to rotate; it seems fine, no problem there. 2. The water pressure fluctuates by 0.1 MPa, which is quite normal – what’s not normal about that? Bro, I don’t see anything unusual here
It has nothing to do with pressure; it’s about whether the installation method is appropriate
Personally, I think it is related to stress. The water flow drives the turbine blades to rotate; in fact, it is the momentum of the water flow that causes the blades to spin. This momentum is proportional to the flow velocity and mass, and the mass is related to density, which in turn is affected by pressure. Therefore, at the same flow rate, pressure changes cause density changes, which in turn lead to changes in the rotation speed of the blades, and thus result in changes in flow rate.
Does the density of water change under these operating conditions? ! Should we think about it again?
This post was last edited by cqdfwy on 2018-2-5 12:14. What is the water pressure? You can’t be talking about that 0.1 MPA range of fluctuation, right? Of course, based on the poster’s description, one could assume that the water pressure is not high and therefore won’t have an impact on density, and that’s correct as well ； In principle, it will have an impact.
With turbines, even when measuring volumetric flow rate, the impact of water pressure on density comes into play; such minor fluctuations in water pressure can still affect water density – and people think it’s the temperature. The uncertainty in the turbine’s performance is mainly due to impurities in the water; disassemble it to check for any foreign objects that might be causing obstruction. I remember once repairing the water flow meter in my repair shop; the water came from a reservoir in the eastern suburbs of the city. When I disassembled it, I found dead fish as well as live shrimps inside, and there were even a few snails stuck to the walls of the pipe, not to mention sand and scale.
Even if all external conditions are ideal and all values remain constant, the turbine itself still has physical gaps as well as instantaneous deformations; as a result, there are errors in the accuracy of flow measurement, along with uncontrollable and uncertain errors. This is nothing surprising at all. I remember that in the past, manufacturers would specify a measurement accuracy of ±4% for turbine flowmeters; I’m not quite sure what the current specified accuracy is.