User Guide
PROCESS CONNECTIONS - Differential Pressure Recorder
The ¼-inch-18 NPT piping connections of the differential pressure unit when viewed from the rear of the recorder are as
follows:
High pressure on the right hand side marked +
Low pressure on the left hand side marked -
The following practices should be followed on all flow and liquid level DPU piping.
1. The distance between the primary device and the DPU should be as short as possible. Distances exceeding 100
feet are not recommended. For distances up-to 15 metres (50 feet) use ¼-inch or 3/8-inch pipe or tubing. For runs
of 15 to 30 metres (50 to 100 feet) use ½-inch pipe or tubing. This recommended distance limitation does not
apply if an air-purge or blow system is used.
2. Slope all piping at least 25mm per linear 305mm (1-inch per linear foot) to avoid liquid or gas entrapment.
3. If process media exceeding 93°C (200°F) is to be measured provide two feet of un-insulated piping between the
primary device and the DPU for each 38°C (100°F) in excess of 93°C (200°F).
4. When steam tracing is necessary, the steam pressure should not exceed 35kPa (5 psi) and insulation should not
be used. If pressure above 35kPa (5 psi) is required, limit the length of tubing around the DPU to two turns and do
not insulate. The temperature of the DPU must never exceed 93°C (200°F).
5. Severe pulsation will affect the accuracy of the instrument. The installation of a pulsation dampening device
upstream of the run is recommended when flow is being measured.
6. Minimise vibration by mounting the instrument on a secure support.
7. Measurement errors can be caused by leaks in the pipe joint; make up all joints using a suitable pipe joining
compound
8. The DPU has two pressure connections in each housing for easy connection to the differential pressure source
with a manifold to facilitate operation and checking.
9. Locate shut-off and by-pass valves easily accessible to operator from the front of the instrument. The block valve
should be the first valve from the process line or vessel.
ACCESS TO THE RECORDER
To open the door, unlock the door lock by inserting the key and turning clockwise a half turn.
To open the door, rotate the wing handle of the door lock a quarter turn anticlockwise.
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