Valve design

Other above-ground continuous flow systems have been designed and operated for SCWO processes. A system developed by ModeU Development Corp. (Modec) uses a tubular reactor and can be operated at temperatures above 500°C. It employs a pressure letdown system in which soHd, Hquids, and gases are separated prior to pressure release. This simplifies valve design and material selection on the Hquid leg. 

Although it has been common practice to specify the pressure loss in ordinary valves in terms of either equivalent length of straight pipe of the same size or velocity head loss, it is becoming more common to specify flow rate and pressure drop characteristics in the same terms as has been the practice for valves designed specifically for control service, namely, in terms of the valve coefficient, C. The flow coefficient of a valve is defined as the volume of Hquid at a specified density that flows through the fully opened valve with a unit pressure drop, eg, = 1 when 3.79 L/min (1 gal /min) pass through the valve... 

Valve Application Technology Functional requirements and the properties of the controlled fluid determine which valve and actuator types are best for a specific apphcation. If demands are modest and no unique valve features are required, the valve-design style selection may be determined solely by cost. If so, general-purpose globe or angle valves provide exceptional value, especially in sizes less than 3-inch NFS and hence are very popular. Beyond type selection, there are many other valve specifications that must be determined properly in order to ultimately yield-improved process control. 

Rotaiy stem-valve designs are normally offered only in their naturally occurring characteristic, since it is difficult to appreciably alter this. If additional characterization is required, the positioner or controller may be charac terized. However, these approaches are less direct, since it is possible for device nonlinearity and dynamics to distort the compensation. 

The DOT rules require that pressure cars have rehef valves designed to hmit pressure to 82.5 percent (with certain exceptions) of test pressure (110 percent of maximum operating pressure) when exposed to fire. Appendix A of AAR Specifications de s with the flow capacity of rehef devices. The formulas apply to cars in the upright position with the device discharging vapor. They may not protec-t the car adequately when it is overturned and the device is discharging hqnid. 

All drum filters (except the single-compartment filter) utilize a rotary-valve arrangement in the drum-axis support trunnion to facih-tate removal of filtrate and wash hquid and to allow introduction of air or gas for cake blowback if needed. The valve controls the relative duration of each cycle as well as providing dead portions of the cycle through the use of bridge blocks. A typical valve design is shown in Fig. 18-121. Internal piping manifolds connect the valve with various sections of the drum. 

Design for automatic isolation of associated equipment via quick closing valves Design system to contain overpressure if practical Install prescrubbers/condensers to reduce load in duct... 

In recent years new ec]uipment has been invented, chemical processes, piping materials, valve designs, and new teehnologies not eonsidered when these formulas were developed with eold water in the 19th century. There is a need to measure the aetual losses onee an industrial plant is eommissioned and operations begin. I he authors of this book have developed a formula that permits the measurements of these losses in a live functioning system. Here it is ... 

For any control valve design be sure to use one of the modem methods, such as that given here, that takes into account such things as control valve pressure recovery factors and gas transition to incompressible flow at critical pressure drop. 

This is just one example of the many compromises the engineer faced with while designing the compressor. The subject of valve design is involved and complex. For individuals wishing to obtain more infoi mation on the subject, references discussing additional aspects of valves are included at the end of the chapter [2, 3, 4, 5, 6. ... 

Davis, H., Effects of Reciprocating Compressor Valve Design on Performance and Reliability, Presented at Mechanical Engineers, London, England, October 13, 1970 (Reprint, Worthington Corp., Buffalo, NY). 

Some transfer valves block flow better than others, making it nccos sary to evaluate the design chosen. Valve design and manufacturing technology has improved to the extent that leakage should not be the problem it onev was. 

Vacuum breaker, 291 Vacuum pump, 9 Vacuum service, 10 ejectors in, 11 liquid pi.ston, 9 liquid piston, 130 sliding vane, 10 Valve design, 62 Valve loss, reciprocating, 62 Valve unloader, 81 Valve velocity, 62 Valves... 

Singh, K. P. and K. K. Niyogi - editors, Heat Exchange Equipment and Valve Design and Operability Improvement, International Joint Power Generation Conference, Pheonix, AZ, 1994. 

In PR valve design, it is desirable to select a PR valve discharge location at a low enough pressure to permit designing for critical flow conditions, so that the relieving rate will be independent of minor back pressure fluctuations. 

We later learned that water valves with lever handles (frequently seen in hospitals or in sinks intended for disabled persons) are designed for the lever to be pushed away from the user to close the valve. Thus, the cold water valve designed for a lever will turn to the left to close. If a round handle is fitted instead of the lever. . . splash ... 

At lower velocities the valve has less pressure drop and thus has less maintenance associated with it. Velocities calculated from this equation can be used to compare valve designs. 

In production facility design, the most common relieving conditions are (1) blocked discharge, (2) gas blowby, (3) regulator failure, (4) fire. (5) thermal, and (6) heat exchanger tube rupture. Relief valve design How rates are commonly determined as follows. 

I) This p irt of each valve designation is always V, which stands for valve. ... 

The fourth part of each valve designation is a 2-, 3-, or 4- digit number indicating the highest ANSI or API cla.ss for which the valve can be used ... 

The fifth part of a valve designation, when used, is a modifier that distinguishes between two or more valves that have the same type and pressure rating but that are considered separately for some other reason. 

Internal pressure P (absolute) at failure. (A typical BLEVE is caused by a fire whose heat raises vessel pressure and reduces its wall strength. Safety-valve design allows actual pressure to rise to a value 1.21 times the safety valveopening pressure.)... 

SAFETY VALVE DESIGN OPERATIONAL CHECK SHEET... 

Figure 7- l4. Safety valve design operational check sheet. Adapted and added to by permission, N. E. Syivander and D. L. Kiatz, Design and Construction of Pressure Relieving Systems, Univ. of Michigan Press, Ann Arbor (1948). Six items of overpressure list above by this author and from API Rec. Practice 521 (1982). 

The valve plates, discs, and springs are mounted in a valve cage, which is inserted in the cylinder. Valve breakage occurs due to fatigue of the metal or improper action. This requires replacement and an evaluation of the materials of construction as well as the basic type of valve. Each manufecturer presents his valve design to match his equipment. Only experience can determine which type of valve works best in a given application... 

Figure 12-6I. Dresser-Rand HPS proprietary valve design, using proprietary blend of PEEK, an advanced non-metallic valve plate material, allowing for temperature ranges greater than previously available nonmetallic plate materials, for lubricated and nonlubri-cated applications for long life. (Used by permission Form 85084, 1992.

Figure 12-6J. Variety of standard and special valves designed and fabricated by the Hoerbiger Corporation. Many of these designs are used in compressor manufacturer s cylinder designs, and some valves have been designed by the compressor manufacturer. (Used by permission Bui. V-100A, 1993. Hoerbiger Corporation of America.)...

Figure 12-17B. Effects of clearance volume on performance efficiency of reciprocating compressor cylinder (valve design effect). (Used by permission Livingston, E. H. Chemical Engineering Progress, V. 89, No. 2, 1993. American Institute of Chemical Engineers, Inc. All rights reserved.)...

Cg,. = compression efficiency, the product of adiabatic and reversible efficiencies, which vary with the cylinder and valve design, piston speed, and fraction values range from 0.70-0.88 usually. 

The valve loss 1 is the loss due to the flow of fluid back through the valve during closing. This is of the order of 0.02 to 0.10 depending on the valve design. 

The dump valve is a very important feature of the positive displacement motor. The positive displacement motor does not permit fluid to flow through the motor unless the motor is rotating. Therefore, a dump valve at the top of the motor allows drilling fluid to be circulated to the annulus even if the motor is not rotating. Most dump valve designs allow the fluid to circulate to the annulus when the pressure is below a certain threshold, say below 50 psi or so. Only when the surface pump is operated does the valve close to force all fluid through the motor. 

There are a number of different clip-on valve designs used by LPG distributors and care is necessary to ensure that only the correct mating regulator is employed. 

Above 1000 Flow through valves may become critical factor Larger pump size selection run at reduced speed-e.g. 3 X size at 1000 cenhistokes running at one-third speed. Modification of valve design may be desirable for higher viscosities... 

There are four basic valve designs used in these compressors finger, channel, leaf, and annular ring. Within each class, there may be variations in design, depending upon operating speed and size of valve required. 

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