Problems with using differential pressure transmitters to measure liquid levels

Why is there no isolation fluid? Water is also a lubricant! At the lowest liquid level, the pressure in the positive-pressure chamber is h_min × ρ, while the pressure in the negative-pressure chamber is h × ρ_water; the resulting differential pressure is therefore h_min × ρ – h × ρ_water = –(h × ρ_water). At the highest liquid level, the pressure in the positive-pressure chamber is h_max × ρ, and the pressure in the negative-pressure chamber is h_max × ρ_water; the differential pressure in this case is h_max × (ρ – ρ_water). At any given liquid level, the pressure in the positive-pressure chamber is h × ρ, and the pressure in the negative-pressure chamber is h × ρ_water, giving a differential pressure of h × (ρ – ρ_water). Let’s look at the relationship between the medium density and the water density.

Thanks! I know my skills are limited; is it more or less what this diagram shows? I’ll send it over for you to take a look

Thank you. I realize my understanding is limited; do you think it means more or less the same as what this diagram shows?

Firstly, this is a problem related to the operation of the instruments on site. You should have two condensers there – one for positive pressure, marked H, and one for negative pressure, marked L. When filling the condensers with water, you need to close the valve at the front of the condenser first, then open the valve you indicated, followed by closing the three-valve assembly of the differential pressure level gauge. Only after that can you start filling with water in order to expel any gas from inside; only liquid should be present. The bolts on the condenser tank above should be wrapped with PTFE tape to ensure a proper seal.

There’s no need to worry about anything else; just close the root valve at the connection point between the condensation tank and the equipment, and that’s it… When zeroing out, fill the tank with a bit more water, then open the root valve to send the excess water back into the tank… What those people upstairs said about having condensation tanks on both the positive and negative pressure sides is complete nonsense. It’s possible to design such systems for the negative pressure side, but as for the positive pressure side, it’s more practical to use radiators instead. You only need to consider safety issues; also, when calibrating the zero point, pay attention to the sequence of operations. I’ll briefly explain that sequence of operations – just be careful about safety... 1. Close the valves of the five-valve assembly (or three-valve assembly) for the pressure transformer, but open the valve of the negative pressure side that leads to the transmitter (the valve on the side of the three-valve or five-valve assembly) ； Close the valve at the base of the condenser tank (the valve between the tank body and the condenser tank) ； 2. Close the root valve on the high-pressure side of the pressure transformer (the valve between the pressure transformer and the tank). 2. Open the filling bolt at the top of the low-pressure side condensation tank, and fill it with water – add a little more than enough so that the liquid level is above the height of the pressure transfer pipe from the condensation tank to the tank. 3. Tighten the liquid injection bolt, open the valve at the base of the condenser tank, wait for about 1 minute until the condensate from the pipeline connected to the side of the tank flows into the tank, and then close the base valve. 4. Open the filling bolt again, and open the drain valve of the five-valve assembly on the positive pressure side (or the drain valve on the transmitter body of the three-valve assembly), so that the sensor diaphragm on the positive pressure side can come into direct contact with air. 5. Perform zeroing in this state. 6. Close the discharge valve on the positive pressure side, tighten the filling bolt, open the valve at the base of the condenser tank, and open the base valve on the positive pressure side. Note: Do not open the connection valve during the process, remember this!