Discharge settled water while helping retain the separate lighter product in your storage tank.
Water can accumulate beneath petroleum or other lighter, immiscible liquids in a storage tank. As a water draw-off approaches the interface, continued discharge can send valuable product into the drainage system.
A correctly selected Belfield valve allows the heavier phase to pass and responds mechanically when the lighter phase enters its chamber. Its calibrated float closes the main discharge at the phase change.
This is a duty for already settled liquids. Emulsified oil and water, significant solids and wax need a separate review of the separation and drainage arrangement.
Immiscible liquids must separate in the vessel before they reach the valve. The valve does not break an emulsion.
The calibrated float rises in the heavier liquid, allowing that phase to flow through the main discharge.
As the lighter phase arrives, the float drops and the mechanism closes the main outlet to help retain that phase.
Tank-bottom water removal and floating-roof rainwater drainage have different pipework and operating conditions.
Water beneath stored product is discharged from the reviewed low-point arrangement. Selection uses the oil and water properties, available head and required drainage rate.
Rainwater travels through the roof drain or hose to the tank-side outlet. A reviewed Belfield arrangement can respond if lighter oil enters through a failed drain component.
Provide the minimum and maximum water head, the product specific gravity and viscosity at operating temperature, and the destination of the discharge. Include any downstream restrictions, pumped operation, solids or wax.
For floating-roof service, the brochure describes an anti-siphon flooded-outlet arrangement using a swan neck. Suitability depends on the roof-drain design and valve configuration; it is not a substitute for checking the drain and hose.
Identify both phases, their specific gravities and viscosities at operating temperature. Include solids, emulsions and wax where present.
Provide minimum, normal and maximum temperature and pressure, required flow, available head and downstream backpressure.
Include connection sizes, wetted-material and seal requirements, the discharge route, and a vessel or P&ID sketch.
A repeatable record makes it easier to discuss a drainage problem with PMA. Use the same observations each time, taken through your site’s established operating and sampling arrangements. This review framework helps organise the evidence; the valve’s operating manual remains the source for its operating procedure.
Identify the tank, product or batch, date and time. Note the temperature, time since the last transfer or mixing event, and available settling time. Include the water-level observation if your site already has a suitable measurement method.
These details give the next drainage record a useful point of comparison.
Record the drainage duration and measured or estimated water volume. State the units and how the quantity was obtained, so an estimate is not mistaken for a meter reading.
Note available tank head and any known change in the receiving system. A slower cycle under different conditions needs context before it is treated as a valve problem.
Record how the end of water draw-off was identified and whether unexpected product was observed downstream. Where an approved sample was taken, include its location, time and result alongside the drainage record.
A record of valve closure and a result for water quality answer different questions. Keep both observations distinct.
Compare cycles with similar products, temperatures and drainage arrangements. Note any change in deposits, residual water observations or downstream conditions, rather than comparing duration alone.
Send PMA the record with the current valve model and drainage sketch when asking for an application review. Include what changed and when it changed.
The valve controls discharge of separated liquid phases. Confirming what is in the discharged water is a separate measurement task.
The float is selected for the liquid pair and operating conditions. A change in product or separation behaviour can therefore matter to the drainage review. Ask PMA to assess that change against the existing selection.
Mechanical closure does not establish an oil concentration or demonstrate that the water meets a discharge requirement.
Explain what the measurement needs to establish, which oil or contamination is relevant, and where a representative sample can be obtained. A laboratory result and an online oil-in-water reading need to be understood in the context of their methods and samples.
PMA’s oil-in-water guide introduces the measurement methods to discuss alongside your tank drainage arrangement.
PMA has supported process measurement and analysis since 1971. We bring the valve and its application together: the liquids, the vessel, the discharge route and the information your team needs.
Share your process conditions and a vessel or piping sketch. Our team can help you review selection, installation requirements and ongoing support.
Published operation, materials, model capacities and application limits.
Installation and operating guidance for the configured valve and process duty.
Explore the wider Belfield technical library and application background.
No. Distinct liquid phases must form before decantation. The settling process and any emulsion treatment are separate from the valve.
A tank-side outlet arrangement can be reviewed for this duty. The roof drain, hose, outlet flooding and anti-siphon provisions must be considered together.
The float is calibrated for the actual liquid pair. PMA needs specific-gravity and temperature ranges, including the smallest difference expected in service.
Speak to the PMA team about your instruments, reagents or service requirements. Tell us what you need, and we’ll help you find the right next step.
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