Inches of mercury conversion to suction of oil

[PutnamVictor]

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 4" of mercury was from the technical specification on the manufactures site.

"Inlet Vacuum Maximum Continuous Inches Mercury 4"

 

[the old grind]

So 4" of mercury = x" of oil for the math, what the pump can draw, and that's what you have to work with? (also height to self-prime w/o cavitation?)

 

[PutnamVictor]

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 manufactures specification for this pump states "Inlet Vacuum Maximum Continuous Inches Mercury 4 " Even if it affects flow rate and PSI by 25%, it should be fine for what I need.

 

[PutnamVictor]

So 4" of mercury = x" of oil for the math, what the pump can draw, and that's what you have to work with? (also height to self-prime w/o cavitation?)

Yes, will the pump draw a 10w-40 oil horizontally 24" and vertically 18"?

 

[the old grind]

Lift is vertical. 24" horizontal doesn't add to that, teeny bit of line friction that matters less as fluid comes up to temp.

25% should mean the diff between level/gravity input and max lift based on relative level in tank vs length of supply line or location high or low.

Convert 4" Hg to inches of water. This will give a conservative NPSH figure for oil. btw, you got this. :thumbsup:
.

 

[4570Man]

Hot hydraulic oil isn’t that much different from water but what about when it’s 0 degrees? Then it barley flows at all.

 

[the old grind]

10w means viscosity at STP 40 means at op temp, ~180 deg where it's thinner yet.

A 5w-40 would flow better when cold, but these weights work in motors just fine.

 

[RalphVa]

I would not locate the pump any higher than the 18" the manufacturer has it.

FYI, oil s.g. is close to about 0.9.

Vapor pressure is low at pumping temps even as high as 200 F. because oil boiling point is generally a minimum of about 700 F.

NPSH is more or less inlet pressure minus vapor pressure minus suction loses plus head in feet of liquid above pump inlet, in feet of water. That type of pump will have a pretty good suction lift or be capable of low NPSH. The NPSH calcs are done in absolute pressure. Cold water at nearly zero VP would present 34 ft of NPSH at same level as the pump. Most pumps want 25 ft. Yours at 18 inches would lose a foot and a half. It would still have above 25 ft of NPSH.

Cold oil would have the highest suction loss.

Have had to edit this a couple times. Used to do this type of calculation all the time, but I've been retired 22 years now.

Ralph

 

[RalphVa]

Fluid Viscosity Limits @ 230ｰF [110ｰ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.

This is pretty heavy oil, more like about a xxw60 (rated as a motor oil, not at the 100 F most hydro oils are rated at). It could get VERY viscous at cold temperatures. I'd be very leary of raising the pump above the manufacturer's 18 inches. The suction line would need to be fairly large to keep from having a lot of friction pressure drop. I don't think most hydro oils are this heavy, more like about xxw20 rated as a motor oil.

Ralph

 

[the old grind]

ISO 32 hydro works in most tractors in most weather. 15w-40 works fine in my T5C when it's too cold to dig, warms up just fine as expected.



Neighbor is a supervisor for GDL, says they use ISO ("light hydraulic") in all their garbage trucks. They don't get many days off for cold weather.