Question About Pressure Using Vacuum Truck

Vapor pressure - Wikipedia, the free encyclopedia

You're use of terms is confusing.

The maximum pressure you can produce is 14.7 PSI.

Pressure head - Wikipedia, the free encyclopedia

Let me see if I can list some of the missing information....

• hose diameter
• oil viscosity
• elevation
• length
• density
• flow restricting valve orifice
• consultant fee
• flow rate
• leaks

Now other than these missing items to an engineering question there's the obvious bill of sale required to take this product or did you actually hope that we'd help you figure out how to quickly steal oil.

The vacuum transfer type tanker trucks I have worked around have vacuum pop off valves set at around -10 PSI or roughly 20 inches of vacuum at the most.

As outgassing goes that is largely irrelevant given the short term transfer times plus the massive amounts of air being displaced by the pumps as the vacuum pop off valves keep the suction pressures limited when necessary.

Relating to where the point is in the hoses that the conversion from static tank pressure to truck vacuum goes there is no way to calculate it without knowing all the details Redfred mentioned in post 2.

In practical application no one really cares just as long as the truck gets loaded to the capacity it is supposed to.

Vacuum pump as gives suction ; it increases ( hydrostatic ) pressure to fill / transfer oil . Based on distance ( suction power ) and hydrostatic pressure ( level in tank ) , suction falls down at different points . Light components / gas may come , based on the level in tank . Else , we may not expect - unless that is a mixture . Hence , suction power comes down on different conditions - so as to deliver required Qty of oil .

As lyn noted, vapor pressure is the factor.

P3 will 'see' the sum of
- the vacuum's negative pressure
- the hydrostatic head of the oil pumped into the tanker truck
- static head from the elevation of the truck above grade (P3 is lower than the bottom of the truck tank)

That will be a negative pressure, a vacuum, at P3 until the head pressures equal the vacuum. But the oil inside the tank will be exposed to vacuum during the entire filling process.

But even if light constituents vaporize, won't they condense when the loading process is finished, the vacuum is turned off and the tank is vented to atmosphere at which point the pressure rises to atmospheric?

Such recondensation would occur, but some of the volatiles would be pumped out along with the air being evacuated from the truck. This is an interesting issue; I don't know if it would or wouldn't present a problem.

From a practical viewpoint, the pressure profile is not important because it is transient. Both the head pressure in the tank and in the truck will change as the levels change. If you are concerned about the vaporization of light ends, that is a real concern. It is perhaps more related to the style of the vacuum pump. If the pump is a liquid displacement pump, the problem is minor. If the vacuum is produced by air eduction ("super sucker") and the light ends are flammable, the results are disasterous, the air light ends mixture can easily pass through the lower flammable or the lower explosive limit and ignite from the hot engine exhaust pipe/

While some vapor is likely, none of the vaporized components of oil will be above their equilibrium vapor pressure. The hazard associated with this is (1) pteroleum vapors are typically flammable, not merely combustible. This means that whilst these are at the highest concentration in the tanker, and in the pump with respect to oxygen fraction of air being evacuated, there does exist an explosion hazard at the point where the vapor entrained in air leaves the pump, so do be careful. Instead of "pressure profiling" why not simply size the flow meter to match the situation of what a "normal" loading time for the tanker would be? Then set operational limits as to how much vacuum should be on the tanker during loading, i.e. vacuum pop-off or breaker that opens when vacuum is approaching the limits of the tanker.

It looks from the drawing that gravity would work for your transfer with a lot less trouble and fewer gas issues. Granted that is probably way too simplistic.

I know from working with Vac-Con that they place warning stickers all over the units not to use this truck for transfer of flammables.

Going back out to the shop......

Why not just put a positive displacement pump at the outlet of the storage tank?

Tons of positive head and no vacuum.

Obviously, this would be too simple, but I have seen that exact set up all over my home turf in West Texas.

I know I agreed with your answer to use a positive displacement pump, but why not also consider the use of a centrifugal pump? Trouble with paraffin?

Depending on viscosity and vapor pressure of the pumped fluid, PD pumps came to mind.

Most of my pump experience is with low viscosity water solutions with SG of around 1-1.5.

BTW, I have cousins who farm a few sections eest of Brownfield.

Cheers

That is interesting. Back in the early 20th Century my mother's uncle Monroe had 27 sections of ranch land there, from selling the place in Big Spring he was rewarded by the State of Texas in lieu of Texas Ranger pay back in the 1880's.