Slide valves

The slide is located in the compressor casting below the rotors, allowing internal gas recirculation without compression. Slide valve is operated by a piston located in a hydraulic cylinder and actuated by high-pressure oil from both sides. When the compressor is started, the slide valve is fuUy open and the compressor is unloaded. To increase capacity, a solenoid valve on the hydraulic hne opens, moving the piston in the direction of increasing capacity. In order to increase partload efficiency, the slide valve is designed to consist of two parts, one traditional shde valve for capacity regulation and other for built-in volume adjustment. 

FIG. 17-16 Solids-flow-control devices, a) Slide valve, (h) Rotary valve, (c) Table feeder, (d) Screw feeder, (e) Cone valve, (f ) L Valve. 

Either trickle (flapper) or star (rotaiy) valves are effective sealing devices for solids discharge. Each functions with a head of sohds above it. Bottom of the bed discharge is also acceptable via a slide valve with a head of solids. 

The flow of the spent catalyst to the regenerator is typically controlled by the use of a valve that slides back and forth. This slide valve (Figure 4-50) is used to control the catalyst level in the stripper. The catalyst level in tlie stripper provides the pressure head that allows tlie catalyst to flow into tlie regenerator. The exposed surface of tlie slide valve is usually lined with a suitable refractory to withstand erosion. 

Figure 4-50. Catalyst slide valve. (Source Enpro Systems, Channelview, Texas.)...

The flowrate of die regenerated eatalyst to die riser is eommonly regulated dirough die use of eidier a slide or plug valve. The operation of a slide valve is similar to that of a variable orifiee. Slide valve operation is automatie. Its main funetion is to supply enough eatalyst to heat the feed and aehieve the desired reaetor temperature. 

These short times are significant when considering that a standard FCCU slide valve will probably move at 1 in./sec—if it doesn t stick. 

In die original system eonfiguration, die hot flue gas leaving die regenerator was expanded in die double slide valve and orifiee ehamber to atmospherie pressure, and dien passed via die waste heat boiler to die main staek. This mode of operation remains possible following die expander retrofit. 

Controlled catalyst circulation is one of the most important prerequisites for trouble-free operation of the FCC unit. Uniform circulation is ensured by controlling the differential pressure between the reactor and regenerator. The differential pressure in the existing plant is controlled by a differential pressure governor adjusting the position of the double slide valve upstream of the orifice chamber. 

The main flue gas flow was ducted through the expander instead of through the double slide valve. 

At the rated duty point, the differential pressure eontroller is aetive. The inlet eontrol valve and trip valve are eompletely open. The main bypass valve is eompletely elosed and the small bypass valve eontrols the differential pressure. Approximately 96%-98% of the flue gas flows through the expander, with the rest passing through the small bypass valve, orifiee ehamber, and double slide valve to the expander outlet to rejoin the main flue gas flow. 

Under normal operations, the existing differential pressure governor is switehed to manual and the double slide valve is wide open. This valve must be suffieiently opened so that, even in the event of an emergeney expander trip, the entire flue gas flow ean pass through the double slide valve without the regenerator diseharge pressure inereasing to nonpermissible levels. 

The slide valve moves parallel to the rotor axis and changes the area of the opening in the bottom of the rotor casing. This lengthens or shortens the region of compression of the rotor and returns gas to the suction side before compression has taken place. Figure 4-15 shows this in diagram... 

Rgure 4-15. Operation of a slide valve. Courtesy of Mayekawa Manufacturing Company, Ltd.)... 

Figure 4-17. Power demand for flooded screw compressors using slide valve and suction throttling [1]. (Reprinted by permission of the Councii of the institution of Mechanical Engineers from The Place of the Screw Compressor in Refrigeration )...

Variation to the slide valve is the turn valve. The valve functions by turning rather than sliding but has the same effect as the slide valve. The plug is... 

Figure 4-19. Side and top view of slide valve arrangements for low- high- and variable-volume ratio compressors [4].

Model II Regenerator at higher elevation and lower pressure than reactor. Slide valves control catalyst circulation. 

Abschluss, m. Abschliessung closing device, shutoff cutoff, seal, -dichtung, /, seal, -hahn, m. stopcock, -schieber, m. slide valve, -ventil, n. shutoff (or cutoff) valve, -vorrichtung, /. closing device. 

Schieber, m. slide, slider, slide bar, slide valve, carriage shovel pusher, shover damper, -kasten, m. (Mach.) slide box, valve chest. 

In subsequent years, Savery made important improvements that benefited future steam inventions. In June 1699 he demonstrated to the Royal Society a pump with two receivers, each with a separate, hand-controlled steam supply. This ensured improved continuity of operation, allowing one receiver tn operate in its vacuum stage and the other under steam pressure. In 1701, he added two more critical steps a second boiler, avoiding the need to shut down the fire and pump, between stages and he replaced the two interconnected steam cocks with a single valve, run with a manually operated long lever. This may have been the inspiration for the modern slide valve and his inventiveness created, in effect, the world s first feed-water heater. 

Figure 11-21D. Helical rotors refrigerant compressors. (1) Cutaway of a 100-ton intermediate compressor. The intermediate Helirotor compressor has only three moving parts the two rotor assemblies and the capacity controlling slide valve. The general purpose Helirotor compressor has only four moving parts two rotor assemblies, the variable unloader valve, and the step unloader valve. Unlike reciprocating compressors, the Trane Helirotor compressor has no pistons, connecting rods, suction and discharge valves, or mechanical oil pump.

End view showing male and female rotors and slide valve on an 85-ton intermediate compressor. The robust design of the Series R compressor can ingest amounts of liquid refrigerant that would severely damage reciprocating compressor valves, piston rods, and cylinders. (Used by permission Cat. RLC-DS-2, Aug. 1995. The Trane Company.)... 

Most reciprocating compressors have inlet and outlet valves (on the piston heads) that are actuated by a pressure difference. These are called self acting valves. There are some larger multistage reciprocating piston compressors that do have camshaft-controlled valves with rotary slide valves. 

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