Fluid Power Journal

Problem: Vacuum Regulators

I maintain a mobile medical unit (hospital), which is a large semi-truck that opens up to over 1,000 square feet for emergency medical usage. Along with all the X-ray, pharmacy, satellite, oxygen, electronics, electrical, hydraulics, pneumatics, etc., there is a vacuum system with two 5-hp vacuum pumps and receiver. There are eight separate vacuum regulators, one at each bedside with an adjustment from 0 – 200 mm of mercury. The added-on vacuum switch to shut off the lead/lag vacuum pumps is adjusted in inches of mercury absolute, while the electronic control board with low vacuum alarms, etc., reads out in inches of mercury. If one vacuum pump cannot keep up at 20 inches of vacuum, the second pump will also kick in. An alarm sounds when the vacuum drops to less than 15 inches of vacuum.

Question: If the vacuum regulators are turned to -200 mm of mercury, what would the equivalent reading be in the following:

Inches of mercury?_________________

Inches of mercury absolute?_________________

Inches of water column?_________________

MM of mercury absolute?_________________

PSI drop?_________________

Find Out The Solution

1.  7.87 inches of mercury

2.  22.05 inches of mercury absolute

3.  107 inches of water column

4.  560 mm of mercury absolute

5.  3.87 psi drop

Note:  One atmosphere on a standard day at sea level

= 29.92 inches of hg

= 760 mm of hg

= 407 inches of water column

= 14.7 psi

200 mm / 760 mm = X / 29.92 in.
X = 7.87 in. of hg

29.92 (atmosphere pressure) – 7.87 =   22.02 inches of hg absolute

7.87 in. of hg / 29.92 in. of hg = X / 407 inches of H2O)
X = 107 inches of water column

760 mm – 200 mm =    560 mm of hg absolute

29.92 / 14.7 = 2.035 in. of hg per PSI   7.87 / 2.035 =    3.86-psi drop

Deadline past. Not available for submissions.


Edward Day, CFPPS, Norgren, Littleton, CO

Answered Correctly:

Richard Throop, CFPS, CFPMM, CFPMT, Neff Engineering Co., Inc., Fenton, MI

Karl Kersker, CFPS, CFPE, ATK Launch Systems, Pleasant View, UT

Harry Pawluk, Jr, CFPS, Hanco, Inc., Ardara, PA

By Ernie Parker, AI, AJPP, AJPPCC, S, MT, MM, MIH, MIP, MMH,
Fluid Power Instructor, Hennepin Technical College, EParker@Hennepintech.edu

This teaser is printed in the Fluid Power Journal. Those who submit the correct answer before the deadline will have their names printed in the Society Page newsletter and in Fluid Power Journal. The winners will also be entered into a drawing for a special gift.

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