IFPS | Inlet Condition Requirements for Pressurized Reservoir

Ethan Stuart

Total Posts: 3
Joined: 11/10/2018

Posted: 2 years ago

How does a pressurized reservoir affect recommendations for inlet conditions?

The specific case in question is lubricating oil for a screw compressor, drawn from a gas-oil separator (ie. pressurized reservoir). The gas-oil separator operates at 130 psi, and the pump increases this by a further 35 psi.

Looking at the Hydraulic Specialist Study Manual Outcome 3.3.2, it seems to me that cavitation from pulling a vacuum is very unlikely to happen at operating conditions (although start up from an unpressurized reservoir is still a concern). Therefore the inlet velocity maximum (1.2 m/s) can be relaxed and the inclusion of a suction strainer is less of a concern.

Would aeration also be less of a concern due to the high tank pressure and low pressure rise over the pump? Aeration is managed by oil retention time, but is it also affected by surface area of the gas-oil interface? That is, given the same amount of oil, would a wide tank be more effective at reducing aeration at the pump than a tall tank?

Looking at the Hydraulic Specialist Study Manual Outcome 3.5.2, cylindrical and centrifugal reservoirs are suggested to improve the removal of gas from the oil. How can the efficacy of these options be judged? Is CFD analysis required?

sfyha agfyya

Total Posts: 1
Joined: 5/12/2026

Posted: 4 days ago

#251 Quote

Ethan Stuart wrote:

How does a pressurized reservoir affect recommendations for inlet conditions?

The specific case in question is lubricating oil for a screw compressor, drawn from a gas-oil separator (ie. pressurized reservoir). The gas-oil separator operates at 130 psi, and the pump increases this by a further 35 psi.

Looking at the Hydraulic Specialist Study Manual Outcome 3.3.2, it seems to me that cavitation from pulling a vacuum is very unlikely to happen at operating conditions (although start up from an unpressurized reservoir is still a concern). Therefore the inlet velocity maximum (1.2 m/s) can be relaxed and the inclusion of a suction strainer is less of a concern.

Would aeration also be less of a concern due to the high tank pressure and low pressure rise over the pump? Aeration is managed by oil retention time, but is it also affected by surface area of the gas-oil interface? That is, given the same Crossy Road amount of oil, would a wide tank be more effective at reducing aeration at the pump than a tall tank?

Looking at the Hydraulic Specialist Study Manual Outcome 3.5.2, cylindrical and centrifugal reservoirs are suggested to improve the removal of gas from the oil. How can the efficacy of these options be judged? Is CFD analysis required?

Yes, with a 130 psi pressurized reservoir, cavitation risk is much lower because the pump inlet has high absolute pressure and plenty of NPSH. Suction velocity limits and suction strainer concerns can therefore be relaxed somewhat, though startup without pressure is still important.

Higher tank pressure also reduces aeration by suppressing bubble growth and keeping gas dissolved in the oil. A wide, shallow tank generally deaerates better than a tall narrow one because it gives more surface area and lower oil velocity.

Cylindrical or centrifugal reservoirs help separate gas by improving flow patterns or using centrifugal force. In most cases, empirical design methods and testing are enough CFD is only needed for difficult or highly optimized systems.

Catherine Jimenez

Total Posts: 2
Joined: 5/15/2026

Posted: 1 day ago

#252 Quote

Ethan Stuart wrote:

How does a pressurized reservoir affect recommendations for inlet conditions?

The specific case in question is lubricating oil for a screw compressor, drawn from a gas-oil separator (ie. pressurized reservoir). The gas-oil separator operates at 130 psi, and the pump increases this by a further 35 psi.

Looking at the Hydraulic Specialist Study Manual Outcome 3.3.2, it seems to me that cavitation from pulling a vacuum is very unlikely to happen at operating conditions (although start up from an unpressurized reservoir is still a concern). Therefore the inlet velocity maximum (1.2 m/s) can be relaxed and the inclusion of a suction strainer is less of a concern.

Would aeration also be less of a concern due to the high tank pressure and low pressure rise over the pump? Aeration is managed by oil retention time, but is it also affected by surface area of the gas-oil interface? That is, given the same amount of oil, would a wide tank be more effective at reducing aeration at the pump than a tall tank?

Looking at the Hydraulic Specialist Study Manual Outcome 3.5.2, cylindrical and centrifugal reservoirs are suggested to improve the removal of gas from the oil. How can the efficacy of these options be judged? Is CFD analysis required fnaf?

With a pressurized reservoir like that, cavitation risk on the inlet side is definitely much lower during normal operation because the separator pressure provides positive suction head to the pump. Startup conditions are usually the more critical case, especially before full system pressure is established.

I’d also agree that aeration behavior changes quite a bit under pressure. Higher tank pressure generally helps suppress bubble growth, but retention time and flow path inside the separator still matter a lot. In practice, wider tanks often help separation because they reduce fluid velocity and increase residence time at the gas-oil interface.

For evaluating cylindrical or centrifugal reservoir designs, CFD can help, but many systems are validated empirically with residence time, deaeration performance, and measured inlet conditions. CFD is useful if you’re optimizing geometry or dealing with persistent aeration issues.

Inlet Condition Requirements for Pressurized Reservoir

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