pump volumne consideration

Page 1 The International Fluid Power Society ALL ABOUT AIR – WHITE PAPER #19, Plumbing & Volume © by Thomas W. Kreher, Applied Pneumatic Controls 6/6/2007 If you are responsible for maintenance you no doubt know the number of square feet in your manufacturing area, the size or horsepower rating of your compressor. There is talk about leaks in compressed air systems, the cost of compressed air, the size of various pipe, hoses and tubing. One thing that seems to be an unknown in many cases is the volume of compressed air that is inside the plumbing in the compressed air system. It is very simple and relatively inexpensive to find out. Most of the compressed air within the plumbing provides a reservoir effect, albeit rather leaky. Reasons you may wish to know the internal volume of a compressed air system are: 1. Safety A. How long would your system operate after a compressor failure? B. How long would you system withhold air if a blow down were desired? C. How long would compressed air drive the sprinkler system? 2. Cost A. What would it cost to replace your compressed air plumbing? B. What would the pay back period be for increased plumbing sizes? C. Would larger plumbing provide reserve air without added reservoirs? 3. Testing leak rate Considerations: Safety:    1A. Rubber hoses should have air fuses to stop hose whip and pressure loss. 1B. Some regulators trap air when the supply is dumped. Test lockout/tagout locations. 1C. Protect against specific contingency with dedicated reservoirs or other means. Cost    2A New plumbing could improve productivity, even save additional compressors. 2B If updating or replacing damage, better pressure and less leaks repay cost rapidly. 2C Over size plumbing can replace reservoirs more efficiently & reduce record keeping. To accurately determine pressure drop and loss of compressed air to leaks it would be helpful to know the volume in the plumbing itself. Boyles Law, P1 x V1 = P2 x V2, provides an inexpensive method to determine this volume. Please see the diagram at the bottom of this page Page 2 The International Fluid Power Society For example use these numbers: 6/6/2007 1. At the outlet of the main reservoir add a full flow ball or butterfly valve (Gate valves would work with consideration for multiple turns to open and close. 2. Tee in a 1” or larger line with shut off just downstream of the main reservoir valve. 3. Connect this line to a 30 gallon (4 Cubic Foot) pressure rated tank or reservoir. 4. Vacate any pressure in the 30 gallon tank and close dump valve. 5. The 30 gallon tank should have an accurate pressure gauge or transducer. 6. Close the outlet valve at the main reservoir. 7. Observe the pressure in the main line and rapidly (to prevent leaks from changing the plumbing volume) open the valve from the main line tee into the 30 gallon tank. 8. Record the high pressure in the 30 gallon tank before it begins to decay. P1 is the system pressure. V1 is the unknown plumbing volume. P2 is the test tank pressure observed. V2 is the volume or the test tank plus V1. P1 = 100 psig P2 = the observed pressure, say 67 psig V1 = ? unknown V2 = V1(?) + 4 Cubic Feet P1 x V1 = P2 x (V1 + 4) Then, P1 / P2 = 100 / 67 = (V1 + 4) / V1 & 1.49 -1 = 4 /V1 V1 = 4 / .49 or V1 = 8.16 Cubic Feet of Volume Record carefully and act rapidly to minimize the leak factor. If the volume in the plumbing is great the pressure observed in the test tank will be high. If the pressure observed in the test tank is very small the volume in the plumbing is small. Possibly for the first time you now know the volume of the plumbing in your work area. This will change a bit from time to time around the core value you have just recorded. In another White Paper, leak test calculation will add the plumbing volume to the test.