JIELI ORIGINAL ENGINEERING NOTES
Thermal Oil Cold Filling: When Pump Cycling Helps Air Venting
Use controlled pump operation to assist cold venting only when the pump, piping and heat-source conditions allow it.
Controlled, intermittent circulation-pump operation can help release trapped air during cold filling of some thermal oil systems. It is a commissioning technique to evaluate for the actual pump and piping, not a requirement to start and stop every pump frequently.
This guide addresses cold filling and air venting in a thermal oil heater system. The term thermal oil boiler is also used for this equipment; thermal fluid heater is a broader product term that includes oil-based heaters. Here, the procedure concerns the oil circulation circuit and must be confirmed for the actual pump, fluid and venting arrangement.
JIELI’s field observation is that alternating circulation and a pause can help gas move toward available vent points, especially with cold oil. The benefit depends on the route out of the system: repeated pump starts cannot correct a trapped high point with no effective vent.
Start with a cold, non-heating system
Use this approach only within an approved cold-filling or cold-venting procedure. Disable the heat source and confirm that no residual heat requires continued circulation. Low process demand by itself is not enough: a hot furnace, refractory or biomass fuel bed can continue transferring heat after firing has stopped.
During heating, dehydration or hot cooldown, maintain the circulation required by the heater manufacturer. Do not interrupt that flow to chase an air pocket. Do not bypass low-flow, low-level or temperature protection to make a pump continue running.
Why a run-and-pause approach may help
A period of circulation can carry free air out of passages toward a separator or high-point vent. A controlled stop changes the local flow conditions; where the geometry permits, buoyancy can then allow gas to rise and collect for removal. A subsequent start may move the remaining gas onward.
The available expansion tank, oil–gas separator and vent connections determine whether that gas has an exit. The technique does not guarantee removal from every downward section, and it is not a method of removing water from oil.
Checks before the first circulation run
- Fill and vent the pump casing and seal area as required by its own manual. A brief dry run can still damage a seal.
- Confirm pump rotation, the approved valve line-up and an open circulation path.
- Maintain the specified cold oil level and flooded suction conditions.
- Identify the designated vent points and safe collection arrangements.
- Check permitted motor starts per hour, starting method and restart delay with the pump and motor supplier.
Fulton’s FT-C manual separates filling, pump preparation and cold circulation. It includes a short pump run followed by a stop in a particular seal-priming procedure; that equipment-specific instruction does not establish a universal pump-cycling schedule. Reference: Fulton FT-C manual, sections 3.5.1 and 3.6.2.
Use observations to decide whether another cycle is useful
With the heat source disabled, observe suction and discharge pressure, flow indication, tank level, pump noise and leakage during the approved run. After a controlled stop, allow the system to settle and use only the designated venting provisions under the applicable safe procedure. Do not loosen an arbitrary flange or hot, pressurised connection.
Recheck oil level and pump priming before a restart. Record whether pressure and flow become steadier and whether air release decreases. Stop repeated cycling if it does not improve those observations; investigate inadequate static head, blocked strainers, leaking suction connections or trapped high points instead.
There is no general instruction to run for a fixed number of seconds or repeat a fixed number of times. The approved procedure must respect the motor’s start limit, pump lubrication and the hydraulic response of the actual installation.
Prove stable circulation before moving to heat-up
Completion of cold venting requires a stable cold level and repeatable circulation without evidence of ongoing air ingestion, not merely a quiet pump for one moment. Restore the normal operating valve positions, check protection and retain the readings as a baseline.
If moisture is present, proceed only with the separate thermal oil heater startup and dehydration procedure. For unresolved suction problems, review the pump’s flow, suction and NPSH requirements.