Inches of mercury conversion to suction of oil

[PutnamVictor]

I'm looking at a Hydro-Gear pump that states a continuous inlet vacuum of 4 inches of mercury. That converts to 54 inches of water. So since oil is lighter than water, can I place the pump 54" above the tank?

My uncertainty is that I'm not taking into account the viscosity difference, the diameter of the suction line, or even something else?

 

[Dave M7040]

I'm looking at a Hydro-Gear pump that states a continuous inlet vacuum of 4 inches of mercury. That converts to 54 inches of water. So since oil is lighter than water, can I place the pump 54" above the tank?

My uncertainty is that I'm not taking into account the viscosity difference, the diameter of the suction line, or even something else?

Pump design/application involves a parameter called NPSH for Net Positive Suction Head.

This link is to more detailed explanations.

https://www.pumpschool.com/applications/NPSH.pdf.

In simple terms, a pump will operate best if it is not struggling to get adequate fluid flow into its inlet. The important term is POSITIVE.

Unless you have the experience and skill to do the calculations for NPSH, it is best to keep the pump low relative to the fluid level and the connection between the pump and tank large.

Deviate from these simple rules and risk pump damage from cavitation and poor performance.

Dave M7040

 

[PutnamVictor]

Agreed, but that can't be done in this case. The hydro motor, transmission, and tank are one unit out of a Wheel Horse D series. I can't run the pump lower than the tank.

 

[Dave M7040]

Agreed, but that can't be done in this case. The hydro motor, transmission, and tank are one unit out of a Wheel Horse D series. I can't run the pump lower than the tank.

I would think though that the pump is mounted lower than the normal fluid level in the tank.

Dave M7040

 

[PutnamVictor]

From the factory, the pump is 18" above the fluid in the tank.

 

[Dave M7040]

From the factory, the pump is 18" above the fluid in the tank.

You can be assured the factory engineers would have done the appropriate NPSH calculation for the pump/fluid arrangement.

Would the pump inlet location on the tank come from the bottom of the tank?

This would improve the NPSH calculation compared to sucking from the top of the fluid level.

Dave M7040

 

[PutnamVictor]

Yes, the suction line comes from the bottom of the transmission/tank.

 

[repete]

I'm looking at a Hydro-Gear pump that states a continuous inlet vacuum of 4 inches of mercury. That converts to 54 inches of water. So since oil is lighter than water, can I place the pump 54" above the tank?

My uncertainty is that I'm not taking into account the viscosity difference, the diameter of the suction line, or even something else?

I have taught fire service hydraulics for over 40 years so I will throw in my 2 cents.

You say that the pump states a continuous vacuum of 4". Is this the parameter of the test that determined the flow and PSI rating? If you saw 0 inches of mercury vacuum, would you be able to deliver greater than the stated pressure and volume? Is 4" the maximum negative pressure the pump will develop?

You are on the correct path by determining the viscosity as it relates to the friction loss of the suction side plumbing. Remember to add "loss" for a suction strainer, any supply piping and any elbows in the plumbing. Rule of thumb is slow the flow rate (GPM or fluid velocity) and you reduce those parasitic losses which is probably common sense to you.

 

[the old grind]

Question about what fluid is spec'ed for the hydro gear pump. ?? (I wouldn't raise the pump any higher than OEM if possible.)

btw, my Terramite and the HG 3100s in my ZTR call out 15w-40 'diesel motor oil', warmup times are short in cold temps. :2cents:

 

[PutnamVictor]

Question about what fluid is spec'ed for the hydro gear pump. ?? (I wouldn't raise the pump any higher than OEM if possible.)

btw, my Terramite and the HG 3100s in my ZTR call out 15w-40 'diesel motor oil', warmup times are short in cold temps. :2cents:

Fluid Viscosity Limits @ 230°F [110°C]
Optimum SUS [cSt] 70 [13]
Minimum SUS [cSt] 55 [9]

This is not an OEM pump. It's actually a variable displacement piston pump. There will be lots of body, and hydro modification to this tractor.