The effect of measuring symmetric and asymmetric capillary tube pressure
Important points in choosing and installing a pressure difference level gauge with a flood diaphragm that we need to know
Symmetrical capillaries
- Temperature effect:
If the ambient temperature rises, capillary V tends to exert force on the DP flood diaphragm (both sides). If both capillaries have the same properties (volume, capillary thickness , fluid filling, and length) are the same, all the resulting forces on the DP flood diaphragm will be zero (Figure DP flood diaphragm position below).
2. Hydrostatic pressure:
The shape of the hydrostatic pressure is below P = ρ × g × D (where ρ and g are constant). To increase the ambient temperature, the density ρ decreases. This means that the hydrostatic pressure P is also reduced. This creates a high force (against the force of gravity). The resulting (final) DP flood diaphragm position is shown in the red figure below.
- Temperature effect:
If the ambient temperature rises, the capillary V tends to exert a force on one side of the DP flood diaphragm (the blue DP sealing position in the figure below).
2. Hydrostatic pressure:
The hydrostatic pressure is in the form P = ρ × g × D (where ρ and g are constant). To increase the ambient temperature, the density ρ decreases. This means that the hydrostatic pressure P is also reduced. This creates a high force (against the force of gravity). This compensates for the force of the flood diaphragm. The resulting (final) DP flood diaphragm position is shown in blue.
Limit gauge pressure difference
Floats and tall towers have shown an important measurement challenge. In particular, long vertical distances from valve to valve require long capillary lengths to facilitate installation. As the distance from the tap to the impact increases, the pressure from the head inside the capillary becomes “too large” for fine tuning. The can time response in tanks and tall towers can be the least desirable because the distance through which the pressure signal is transmitted is significantly greater. In general, as the length of the capillary connected to the low transmitter increases, increasing accurate measurement becomes increasingly difficult.
Rose Calibration Company in Melbourne, Australia with over ten years of experience provides all calibration, maintenance, and repair services throughout Australia. If you live in Sydney, Melbourne, Adelaide, Perth, Geelong, and Brisbane, you can receive your quote in less than two hours by fill-up the form via the “Booking” link.