Gauge, pressure, manometers conditions

Under most conditions when measuring the pressure drop of a gas, its density may be ignored, as pm > /on- When the second leg is open to atmosphere, the manometer reading represents the gauge pressure—the absolute pressure will equal the pressure differential plus the barometric pressure. 

Pressure reducing valves should be of steel constmction, designed for minimum and maximum operation conditions. Pressure gauges should be of ak-kon constmction. Pressure rehef valves should be of the spring-loaded type. Rupture disks may be used only as auxkiary equipment. Differential pressure measurements using mercury manometers should be avoided in ammonia service. 

The mechanical phenomena gauges measure the actual force exerted by the gas. They include a U-tube, a capsule dial, a strain, a capacitance manometer, a McLeod gauge, etc. Vacuum is measured according to the displacement of an elastic material or by measuring the force required to compensate its displacement. The measurement ranges from atmospheric pressure to 102 Pa in rough vacuum conditions. 

Example 2.1. A manometer of the type shown in Fig. 2.4 is used to measure the pressure drop across an orifice (see Fig. 8.19). Liquid A is mercury (density 13,590 kg/m ) and fluid B, flowing through the orifice and filling the manometer leads, is brine (density 1260 kg/m ). When the pressures at the taps are equal, the level of the mercury in the manometer is 0.9 m below the orifice taps. Under operating conditions, the gauge pressuret at the upstream tap is 0.14 bar the pressure at the downstream tap is 250 mm Hg below atmospheric. What is the reading of the manometer in millimeters ... 

Figure 4 Medium-high-pressure g.l.c. apparatus. (A) Pressure regulator, (B) pressure gauge, (C) conditioning coll", (D) soap-film flow meter, (E) drying trap (F) conditioning coil (G) sample injector (H) column (I) control value (J) splitter (K) needle valve (L) detector and recorder (M) manometer (N) solute vapour reservoir (0) pressure gauge (P) vacuum pump...

The key tool in troubleshooting flash-zone pressure problems is a vacuum-tower pressure survey. The time to initiate this survey is just after start-up when the trays, demister, and ejector system are clean and in good condition. Pressures are best measured with a portable mercury-filled vacuum manometer. Using a vacuum pressure gauge will reduce the accuracy of observed pressure drops. Relying on permanently installed gauges for pressure drop data will not give reliable results. 

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