There are far too many variables to offer a definitive answer but I would estimate that it probably would be much less than 25ft.
While oil is slightly lighter than water for the purposes of explanation I will use water, given that i have water specs handy and would have to research oil.
The absolute maximum that water can be lifted by means of suction or vacuum is 32.76ft.
If you have an open vessel (or a vessel which is vented to atmospheric pressure) an you attach a vetical column to that vessel, then create a negative pressure in the column the atmospheric pressure pushing down on the surface of the liquid will push the liquid up the column until the static head (physical weight) of the liquid equals atmospheric pressure.
Standard atmospheric pressure at sealevel is 14psi. If the vertical riser were to have a perfect vacuum (-14psi) water would rise in the tube until the static weight of the water equaled 14lbs. The static head of water is 0.434 lbs/vertical ft.
Therefore the absolute maximum water could rise would be:
14psi/ 0.434/lb= 32.76 ft.
While 32.76ft is the theoretical maximum at sealevel, we must also consider that atmospheric pressure drops with increase in altitude or changes in weather conditions and as the atmospheric pressure drops the static head drops proportionally.
The next parameter we must consider is the physical resistance of the pipe or line. Pipe specifications will show the physical linear resistance of the line in lbs/ft. You must compute the length of the line to find the total resistance for the line and deduct that pressure from the vertical column. Fittings on a line offer a substantial increase in resistance, by example a 90 would have the same resistance as an additional 10 feet of line. A 45 would be in the order of 6 ft of line. As you can see, if one were to erroneously attempt to use two 45's to make a radius fitting, it would actually increase the resistance as you would have to allow 6 ft for each 45 deg fitting for a combined resistance of another 12ft as opposed to 10 ft for the 90.
The next problem you encounter is "Pump Cavitation". We are all aware of the fact that water boils at 212degF, but that is an incomplete statement. Water actually boils at 212degF at standard atmospheric pressure at sealevel. As the pressure is decreased the boiling temperature of a liquid decreases dramatically. In a vacuum (-14psi or -29.9in/hg) water boils at 40degF. That is why refrigeration techs pull a vacuum on a system to dehydrate it. As the pressure drops in the system any residual water will boil and be drawn out at standard room temp. Once the vacuum reaches 29.9in/hg is can be assumed all remaining water has boiled out of the system at room temperature.)
In a pump, as the pressure drops below the boiling pressure and temperature for the liquid, the liquid in the impeller section flashes to a gasseous state (steam) and the impellar is no longer able to push the liquid. For that reason pump specifications will often list a minimum static head pressure, which would mean the minimum pressure of the liquid at the inlet of the pump.
For illustration purposes let us assume the minimum "inlet static head" was listed as 10psi. Water weighs 2.34lb/ft vertical, therefore 10psi would be:
10psi/ 2.34psi/vert = 4.27ft.
We would then have to deduct the inlet pressure from the static head pressure of the vertical line.
With zero line resistance the static head at standard atmospheric pressure at sealevel was 32.76 ft, therefore the maximum elevation of the pump would be:
32.76ft - 4.27ft = 28.49ft to prevent cavitation.
Oil is slightly lighter than water therefore the static head of oil would be slightly higher but this would probably be only a fraction of a foot difference, and in no case should a pump be expected to work efficiently at or above 80% of the static head compensated for line resistance.
Also keep in mind that the line resistance is for new, clean pipe. As residual debris collects on the pipe wall line resistance will go up dramatically.
Linear Mode
