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Nitrogen vs Hydraulic Fluid
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Nitrogen or other compressed gas has become more popular for calibration for several reasons:
Compressed gas is more stable than hydraulic fluid. Gas is highly compressed, while hydraulic fluid is an incompressible fluid. Thus, any small change in volume due to leaks or temperature change can make a large difference in pressure with hydraulic fluid. But, because gas is compressed, it will expand to compensate for any volume change and the change in pressure due to leakage is much less.
Compressed gas provides better control of pressure than hydraulic fluid. It is easier to go from one test point to another than hydraulic fluid without overshoot and hysteresis error in a multiple point calibration. It also provides a better range than hydraulic fluid. It can be used at very low pressures of 0.1 inch of water column all the way to 3000 psi, while hydraulic fluid is most effective in the 500-5000 psi range.
Compressed gas is cleaner to use than hydraulic fluid. It leaves no liquid to contaminate a gas system and avoids the problem of fluid freezing in a trapped space. Because it is an inert gas when you vent the nitrogen to atmosphere you prevent the environmental problems associated with spilling liquid.
Hydraulic fluid has other advantages though. For higher pressure calibrations hydraulic fluid is the only option. It also works when the bottle of compressed gas that you are using drops below the test point you are trying to hit. On balance, the benefits of using compressed gas outweigh the problems in most cases. It depends on the situation but often compressed gas provides a better solution for the user.
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The newly redesigned Nitropak:
- We use a light-weight carbon fiber cylinder to reduce weight. It’s the lightest unit on the market with no sacrifice in performance.
- All the valves and pressure control parts are made specifically for this unit
- We use 1/8” stainless steel tubing throughout the Nitropak. This cuts the volume of the internal passages down and reduces the use of nitrogen.
- We use O-ring fittings on all ports. This prevents vibration and thermal changes from loosening the joints.
- The fine adjust piston is large in diameter with a travel of over 50 turns. This provides adjustment of approximately 20-30% of the set pressure which is far better than our competitor’s unit.
- The Nitropak is protected with a burst disk in case of overpressure due to heat or overfilling.
- A steel mounting ring riveted into the case and secured with 16 screws mount the internals of the Nitropak to the case securely enough to handle any rough treatment.
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Ralston Takes to the Road
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Check us out at one of these upcoming tradeshows:
 NCSLI 2008
August 3-7 | Orlando, Florida USA
Booth 110
AGMSC 2008
August 12-15 | Robert Morris College
Moon Twp., Pennsylvania USA
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Did you know that if you are calibrating a pressure instrument you should avoid changing the temperature of the equipment? Although the hose and pump body are silver to help reduce temperature changes, you should hold the pump by the fine adjust knob and the pumping piston to keep your body heat from changing the pressure reading due to temperature change. If you can stay out of the sun it will help stabilize the pressure as well.
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