Discharge control valve

If we cannot open the discharge control valve of a centrifugal pump 100 percent before the FLA point is reached, then we say that the pump... 

It is positively my experience that the most common reason for pumps cavitation is partial plugging of draw nozzles. This problem is illustrated in Fig. 25.5. This is the side draw-off from a fractionator. Slowly opening the pump s discharge control valve increases flow up to a point. Beyond this point, the pump s discharge pressure and discharge flow become erratically low. It is obvious, then, that the pump is cavitating. 

Reading Compressor temperature Suction Discharge Control valve opening, % Remarks... 

Slowly opening the pump s discharge control valve increases flow up to a point. Beyond this point, the pump s discharge pressure and discharge flow become erratically low. It is obvious, then, that the pump is cavitating. 

Check valve failure Blocked discharge Control valve failure Thermal expansion of liquid Heat exchanger tube rupture Reflux failure and overhead system Loss of reboiler heat Venting of storage tank Failure of individual motor Accidental closure of valve... 

Continuous Pressure Filters These filters consist of conventional drum or disk filters totally enclosed in pressure vessels. Filtration takes place with the vessel pressurized up to 6 bar and the filtrate discharging either at atmospheric pressure or into a receiver maintained at a suitable backpressure. Cake discharge is facilitated through a dual valve and lock-hopper arrangement in order to maintain vessel pressure. Alternatively, the discharged filter cake can be reslurried within the filter or in an adjoining pressure vessel and removed through a control valve. 

In controlled venting operation, the quench tank pressure is maintained at a desired level by a pressure controller/control valve system or pressure rehef valve. This mode of operation is used when the discharge mixture bubble point is close to or below the maximum ambient temperature, and it is desired to hmit the maximum quench tank pressure. 

When a pump has a motor drive, the process engineer must verify that the motor will not overload from extreme process changes. The horsepower for a centrifugal pump increases with flow. If the control valve in the discharge line fully opens or an operator opens the control valve bypass, the pump will tend to run out on its curve, giving more flow and requiring more... 

In order to avoid the need to measure velocity head, the loop piping must be sized to have a velocity pressure less than 5% of the static pressure. Flow conditions at the required overload capacity should be checked for critical pressure drop to ensure that valves are adequately sized. For ease of control, the loop gas cooler is usually placed downstream of the discharge throttle valve. Care should be taken to check that choke flow will not occur in the cooler tubes. Another cause of concern is cooler heat capacity and/or cooling water approach temperature. A check of these items, especially with regard to expected ambient condi-... 

Relief valves are often seen to be undersized for the required relieving rate, due either to poor initial design or changes in the process conditions which occurred during design. The most common system problem is that the relief valve was adequately sized for blocked discharge but not sized for the flowrate that could occur as a result of a failure in the open position of an upstream control valve (i.e., gas blowby). See Chapter 13. 

The heat transfer oil control valve was leaking. Unknown to the operators, the boiler temperature rose from 75°C to 143°C, the boiling point of the contents. Finally, bumping in the boiler caused about 0.2 ton of liquid to be discharged through the vent. 

Ps = 168 psi, at pump discharge, using assumed control valve pressure drop of 35 psi... 

The discharge pressure developed hy the compressor must he equal to the process gas s total system resistance, of control valves, hand valves, orifices, heat exchangers, and any other process-related devices through which the discharge gas from the compressor must flow. As this resistance changes, the gas flow through the compressor will automatically adjust itself to equal the new resistance. ... 

Exiting steam from the roof and convection-pass cooling sections is collected in headers and typically passes through a primary superheater tube bundle, where a controlled amount of superheat is provided. In the superheater the steam discharges through an outlet header and across a spray attemperator (which provides the steam temperature control) and is then delivered to the control valves for distribution and subsequent use in a turbine or other items of process equipment. 

In any equipment where an interface exists between two phases (e.g. liquid-vapour), some means of maintaining the interface at the required level must be provided. This may be incorporated in the design of the equipment, as is usually done for decanters, or by automatic control of the flow from the equipment. Figure 5.16 shows a typical arrangement for the level control at the base of a column. The control valve should be placed on the discharge line from the pump. 

It is easy to improperly design a steam trap. The design must work for two circumstances and often a designer will check only one of these. The circumstance often overlooked is as follows On startup or upset, the steam control valve can open wide so that the steam chest pressure (assume for this discussion that we are speaking of a reboiler) rises to full steam line pressure. At a time like this, the steam trap downstream pressure can be atmospheric due to process variations or the operators opening the trap discharge to atmosphere in an attempt to get it working. 

Level control in supracell with pneumatic sensor and clarified water discharge regulating valve... 

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