I thought I would add Instrumentation requirements for the Free Water Knockout below.
Probes/Alarm Float Switches
- If an oil-water interface control probe is used, it should be mounted vertically with an on-line removal fitting, including a full port isolation ball valve. Drexelbrook No. 508–25–6 probes have given good service in this application.
- Two horizontally-mounted probes with on-line removal fittings, including a full-port isolation ball valve, should be used as oil-water interface redundant indicators, installed for high and low level alarms. Babbitt LS–8000–115VAC Halar coated probes have given good service in this application.
- Both high and low liquid level alarm float switches (or probes) should be provided. Where required by government regulations or job specifications, shutdown systems also should be supplied. Protection (shutdown) is desirable to prevent oil emulsion overflows into the gas system and gas blowby into downstream liquid systems. This may vary from field to field, depending upon the equipment arrangement. Microprocessor control is generally the least expensive and most satisfactory system. However, in some remote locations, where electric power is not available, mechanical interface detection and control is the only solution.
- All solenoid valves should be 3-way with a manual override switch and 120 VAC coil.
- Relief valves and level controls should be installed as specified per requirements.
- All instrument tubing should be stainless steel.
- All wiring terminations and devices should be installed in a single panel enclosure, which should also contain all probe electronics. Panel enclosure should be rated for the area classification, but should be NEMA 4X as a minimum. The electronics should be 4–20 mA remote output and local indication.
Low Flow Alarm
- The sand dump outlet line should be fitted with a low flow alarm. The low flow alarm shall indicate when the sand dump system is plugging. This device can also be used to detect leaking sand dump valves.
Temperature and Pressure Control
- Temperature indication should be displayed by one 5 inch dial face thermometer with a stainless steel thermowell.
- Pressure indication should be displayed by one 4½ inch dial face pressure gauge with a ¾ inch ball valve for isolation. A bleeder valve is recommended.
- An instrument air header with adequate regulation for control, minimum NPS ½, should be provided.