@derek-m in the same way as the hp heat meter would be less accurate than the sontex, would the hp pressure reading be less accurate than this dial ? They always read about 0.4 bar different
There is always a problem when the same parameter is measured by two different devices. As far as which is likely to be the most accurate, you would need to look at the specification of the pressure gauge and pressure transmitter.
The pressure gauge in the photo will have a specified accuracy, which is normally quoted as +/- a percentage of FSD (Full Scale Deflection). The pressure gauge has an FSD of 6 bar, so if the true pressure is say 2 bar, and the specified accuracy is say +/- 5%, then the displayed reading could be anywhere between 1.7 bar and 2.3 bar.
The same could be true for the pressure transmitter, which is supplying the reading on the controller display. It is therefore quite probable that there will be a difference between the two readings.
To make matters even more complicated, when measuring the pressure of liquids, it may be necessary to allow for 'head pressure' (this is the pressure that can be exerted by the column of liquid in any vertical pipework) A 10.2 metre vertical column of water will produce a pressure of 1 bar at the bottom end, even though the pressure at the top end may be at atmospheric pressure, so if the pressure at the top end is now increased to 2 bar, a pressure gauge installed at the bottom end would actually indicate 3 bar.
Some of the difference between the two readings could therefore be due to a difference if height, between the pressure gauge and the pressure transmitter.
The actual water pressure in your heating system is not that critical, as long as it is above the minimum specified pressure, and does not exceed the maximum specified pressure. So provided that both indications are above 1 bar and below 2 bar, then your system should be okay. If the pressure starts to fall then it would probably indicate that you have a water leak somewhere.
Re the height difference: The two measuring devices are at different levels but should they be the same in a closed pressurised system ? I’m happy that it doesn’t really matter though !
Re the height difference: The two measuring devices are at different levels but should they be the same in a closed pressurised system ? I’m happy that it doesn’t really matter though !
It is all Isaac Newton's fault, after he discovered gravity, things just kept 'falling down', even water, unless it is in vapour form.
If you mean, should both readings be the same in a pressurised system, the answer is NO if liquid is involved.
If you have an enclosed heating system, where the height difference between the lowest pipework and the highest pipework is 10.2 metres, and you fill the system with water at atmospheric pressure, and then fit two identically calibrated pressure gauges, one to the lowest pipe and one to the highest pipe, the top gauge will read 0 bar and the bottom gauge will read 1 bar. If you now increase the pressure within the enclosed system to 1.5 bar, the top gauge will now read 1.5 bar, but the bottom gauge will read 2.5 bar.
Under most normal circumstances, the bottom gauge will always read 1 bar higher than the top gauge.
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