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Quotes - Engineering - Sales| DUTY | TYPICAL SERIES | CONSTRAINT | PASSES |
| Hydraulic Oil | OC | Pressure drop | 1 and 2 pass |
Hydraulic Oil Cooling
Keeping Oil Temperature Inside Its Working Band
Hydraulic systems convert a proportion of their input power into heat, and that heat has to leave somewhere. Oil that runs above its working band thins, loses film strength, oxidises faster and attacks seals. The OC Series exists for this duty.
Oil is a poor heat transfer fluid. Viscosity is the reason: it suppresses turbulence and thickens the boundary layer. A given flow of oil produces a far lower film coefficient than the same flow of water, which is why the OC range runs to larger shells and longer tube lengths than the general-purpose WU.
Pressure drop is the binding constraint. Oil-side drop rises steeply with both flow and viscosity, and a unit selected on thermal duty alone can be impossible to pump through at the flow the system delivers. This is why the OC range offers 1 and 2 pass arrangements rather than the 4 and 6 pass options found on water duty.
Size against the cold end. Oil leaving the cooler is at its most viscous while the temperature difference is at its smallest, so the last few degrees cost disproportionate surface. Relaxing the outlet target slightly frequently shrinks the unit noticeably.
Cyclic duty needs stating. A press, a quench line or an intermittent machine puts heat into the oil in bursts. Sizing on the average produces a system that runs hot during the shift and cool overnight.
Oil Cooler Selection
Oil flow, temperatures, viscosity grade and the pressure drop available.
Duty Inputs
- Oil flow: GPM through the cooler
- Oil temperatures: In and required out
- Viscosity grade: ISO VG or SAE
- Pressure drop: Allowable on the oil side
Series
- OC for dedicated oil duty
- Shells 8" to 20"
- Tube runs to 144 inches
- 1 and 2 pass arrangements
- Removable bundle
Watch For
- Cold start viscosity
- Cyclic and burst loads
- Pressure drop at design flow
- Cooling water quality
- Outlet temperature target
Related
Oil Duty Is a Pressure Drop Problem
State the Allowable Drop or the Selection Will Be Wrong
This is the single most useful thing you can send with an oil cooling enquiry. Oil-side pressure drop rises steeply, and the difference between an acceptable selection and an unpumpable one is frequently one pass arrangement.
Where the pump or the circuit is already fixed, send what is actually available at design flow. It constrains the selection more than the thermal duty does.
Cold Starts and Bypass Arrangements
Oil at ambient can be many times more viscous than at operating temperature, and forcing cold oil through a cooler produces pressure drop the system was never designed for. Many installations fit a thermal bypass for exactly this reason.
If the system has one, say so, because it changes the flow the cooler actually sees during warm-up and therefore how the selection should be checked.
