Pressure upstream

The so-called hyperbar vacuum filtration is a combination of vacuum and pressure filtration in a pull—push arrangement, whereby a vacuum pump of a fan generates vacuum downstream of the filter medium, while a compressor maintains higher-than-atmospheric pressure upstream. If, for example, the vacuum produced is 80 kPa, ie, absolute pressure of 20 kPa, and the absolute pressure before the filter is 150 kPa, the total pressure drop of 130 kPa is created across the filter medium. This is a new idea in principle but in practice requires three primary movers a Hquid pump to pump in the suspension, a vacuum pump to produce the vacuum, and a compressor to supply the compressed air. The cost of having to provide, install, and maintain one additional primary mover has deterred the development of hyperbar vacuum filtration only Andrit2 in Austria offers a system commercially. 

Pressure Relief Valve (PRV) A relief valve is a spring-loaded valve actuated by static pressure upstream of the valve. The valve opens normally in proportion to the pressure increase over opening pressure. A relief valve is normally used with incompressible fluids. 

In most units, the flue gas pressure is reduced to atmospheric pressure across an orifice chamber. The orifice chamber is a vessel containing a series of perforated plates designed to maintain a given back-pressure upstream of the regenerator pressure control valve. 

For the tandem arrangement gas seal, a primary seal vent must be pro vided to vent the leakage across the process side seal. This vent ma> lie to flare or other suitable gas disposal point. The back pressure under nor mal conditions should be kept to a low value. A small amount of back pressure is recommended to keep a positive differential across the see ondaiy seal. Leakage measurement may be provided in the vent line to provide health monitoring of the primary seal. Unfortunately, the rotameter, which would be the obvious choice, should not be used because of its lack o reliability. If an orifice or needle valve is used to set the back pressure to the seal vent, pressure upstream of the restriction can be measured for a relative flow measurement. This type of reading does provide trend data that may be used to judge the seal s performance. 

Relief Valve - A relief valve is an automatic pressure-relieving device actuated by the static pressure upstream of the valve, and whieh opens in proportion to the increase in pressure over the opening pressure. It is used primarily for liquid service. 

Safety Valve - A safety valve is an automatie pressure-relieving deviee actuated by the static pressure upstream of the valve and characterized by rapid full opening or pop action. It is used for gas or vapor service. (In the petroleum industry it is used normally for steam or air.)... 

The pressure upstream of the suction valve will increase until sufficient back-pressure is established on the wells or equipment feeding the compressor to reduce the flow to a new rate in equilibrium with that being handled by the cylinder or until a flare valve or relief valve is actuated. 

If the outlet or discharge pressure is lowered further, the pressure upstream at the origin will not detect it because the pressure w ave can only travel at sonic velocity. Therefore, the change in pressure dow nstream w ill not be detected upstream. The excess pre.ssure drop obtained by lowering the outlet pressure after the maximum discharge has been reached takes place beyond the end of the pipe [3]. This pressure is lost in shock waves and turbulence of the jetting fluid. See References 12, 13, 24, and 15 for further expansion of shock waves and detonadon waves through compressible fluids. 

These conditions are similar to flow through orifices, nozzles, and venturi tubes. Flow through nozzles and venturi devices is limited by the critical pressure ratio, r,. = downstream pressure/upstream pressure at sonic conditions (see Figure 2-38C). 

P = Totitl pressure at lower end of system, psig Pbr = Barometric pressure, psi absolute Ps = Total pressure upstream (higher) of system, psig... 

Safety-Relief Valve this is an automatic pressure-relieving device actuated by the static pressure upstream of the valve and characterized by an adjustment to allow reclosure, either a pop or a non-pop action, and a nozzle type entrance and it reseats as pressure drops. It is used on steam, gas, vapor and liquid (with adjustments), and is probably the most general tyqDe of valve in petrochemical and chemical plants (Figures 7-3, 7-3A, and 7-4). Rated capacity is reached at 3% or 10% overpressure, depending upon code and/or process conditions. It is suitable for use either as a safety or a relief valve [1,10]. It opens in proportion to increase in internal pressure. 

Figure22.14 Condensate line sizing chart where pressure at traps is above 4bar (SI units). 1. From pressure upstream of trap move horizontally to pressure in return line (A). 2. Drop vertically to condensate load in kg/h (B). 3. Follow curve to RFI scale and across to same return line pressure (C). 4. Move upward to return line flash velocity - say, 25 m/s maximum (D). 5. Read return line size.

Insufficient pressure upstream of the slide valve can be caused by ... 

Equations 1, 3 to 8, involving seven unknowns, may be solved by trial and error to give w = 0.0057. Thus the pressure upstream from the shock wave is ... 

The flow rate of C02 in a 6 in. ID pipeline is measured by an orifice meter with a diameter of 5 in. The pressure upstream of the orifice is 10 psig, and the pressure... 

The thrustor was considered to consist of two sections 1) where the mixture is formed and 2) where combustion takes place and the pressure is generated. The principal mechanism involved in the combustion process was assumed to be successive ignition, but other mechanisms such as turbulent frontal combustion were also considered. The analysis yielded two instability criteria, expressed in terms of the Mach number in zone 1, the velocity ratio in zones 1 and 2, the isentropic exponent in zone 2, the activation energy, the temperature of the cold gas, the pressure upstream of the combustion zone, and the pressure drop due to the combustion... 

Furnace temperatures were measured by two Pt—10% Rh thermocouples. One was mounted next to the suspended substrate samples and the other next to the vapor source. The rate of flow of the dry air through the furnace was determined by measuring the air pressure upstream from a capillary restriction in the air line. The pressure was measured by an oil manometer which had been calibrated against known flow rates of air through the capillary restriction. 

Number of independent equations Number of degrees of freedom Number of independent variables Number of zeros of function Pressure upstream of nozzle in flapper/nozzle system Pressures applied to limbs of manometer tube or pressures downstream and upstream of orifice plate Distillation column pressure Pressure in feedback bellows of pneumatic controller Frictional drag per unit cross-sectional area of manometer tube... 

As an analogy, consider a river with a dam somewhere between its source and its terminus. If the flood gates of the dam are opened, the flow of water transiently increases everywhere in the river. At sites near the end of the river, the increase in the flow can be explained simply by the increased pressure of water coming from upstream at sites near the source, it can be attributed to a reduced pressure downstream. Only at the site of the dam is the situation reversed the flow of water increases here in spite of the fact that the pressure downstream has risen and the pressure upstream has fallen. 

To identify inlet control valve scenarios, the maximum expected pressure upstream of each inlet control valve was compared to the MAWP of the equipment under consideration. 

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