Valve disablers

The second way to unload a reciprocating compressor is with valve disablers. Most of the unloaders you have on your compressors are likely of this inferior type. They typically consist of steel fingers, which are pressed down through the valve-cap assembly. The fingers prevent the valve plate from moving. These valve disablers are far less costly than an adjustable clearance pocket. They may be used on both the crank and head ends of the cylinder. They can reduce the gas flow through a cylinder to zero. 

Unfortunately, valve disablers have a detrimental effect on the adiabatic compressor efficiency. This means that, even though no gas may be moving through the crank end of a cylinder, the piston is still doing work on the gas inside the crank end of the cylinder. If you would like proof, place your hand on the valve cap on such a disabled cylinder. The high temperature you will feel is wasted compression work going to useless heat. I have measured in the field that, after a cylinder end is completely disabled, it is still converting 20 percent of the former compression work to heat. 

The other problem with valve disablers is poor mechanical reliability. They get stuck inside the valve cap, especially in dirty-gas service. Once stuck, the valve—and really the entire end of the cylinder—is out of service, until the next overhaul of the reciprocating compressor. 

Valve disablers Used in reciprocating compressors to reduce capacity. 

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 ... 

With oven 2 disabled by the switching valves or by using a separate instrument with the same column installed as the precolumn above and with the same operating conditions, carry out the following preliminary runs. 

The bonnet opening of the disabled valve body below Tank No. 7 provided a steady stream of fuel to create a blow-torch like flame aimed beneath Tanks Nos. 5, 6, and 7, which threatened the equipment. Within a short length of time, safety relief valves on these tanks opened with a loud shrill sound to cope with the heat-induced rising pressure in the tanks. 

Control device. The control device is mounted in a standard 19" rack. It contains the power snpply for the solenoid valves, the power snpphes for the transducer, a 12 Bit A/D-conveiter and the microcompnter. The microcomputer is equipped with a battery-buffered RAM and a restart logic to restart antorrratically after a power fail. The fairltless operation of the system is controlled by a watchdog. The device is operated by menu, displayed on a 4><40 alphantrmeric LCD-display, and a keyboard with 10 nnmeric kevs, 5 function keys and a key operated switch to disable certain commands. 

The release of methyl isocyanate (MIC) from the Union Carbide chemical plant in Bhopal, India, in December 1984 has been called the worst industrial accident in history Conservative estimates point to 2,000 fatalities, 10,000 permanent disabilities (including blindness), and 200,000 injuries [38]. The Indian government blamed the accident on human error—the improper cleaning of a pipe at the plant. A relatively new worker was assigned to wash out some pipes and filters, which were clogged. MIC produces large amounts of heat when in contact with water, and the worker properly closed the valves to isolate the MIC tanks from the pipes and filters being washed. Nobody, however, inserted a required safety disk (called a slip blind) to back up the valves in case they leaked [12]. 

Possible remedies for PTS events are automatic overpressure protection which disable systems that can pressurize the RPV, adnodnistrative measures to isolate high pressure systems from the primary circuit, and dedicated outage safety valves. It is also possible to mitigate PTS by recovering the material properties of the RPV through thermal annealing. 

Figure 5.3-5a shows that, for heatup, a temperature of 309 F is required before the pressurizer safety valves can be used for overpressure protection without violating any P-T Limits. Figure 5.3-5b shows that, for cooldown, the safety valves cannot be used below a temperature of 225 F. For the temperature interval 140 F above T rpop heatup, as defined by Branch Technical Position RSB S-V, and for the 66 F above op for cooldown, administrative controls would be required ro protect some P-T Limits, particularly the design limit of loo°F/hr. Rather than relying on administrative controls during these temperature intervals, the Tj-. p enable and disable temperatures for System 80+ are defined by the intersection of the controlling P-T Limit (100 F/hr) curve and the pressurizer safety valve setpoint. 

---