Control valves manual

Per application flow control valve, pressure control valve, temperature control valve, level control valve, on- ofT control valve, manual control valve, emergency shutdown valve. 

For air-flow control, the system may contain a control valve or damper that automatically or manually modulates system pressure drop. The dotted curves in Figure 4a on each side of the system resistance curve might represent operating extremes of the system resistance as the control valve is varied from maximum to minimum opening. These curves also intersect the fan curve at desirable operating portions of its range both for efficiency and flow control. 

Pneumatic and hydraulic vibrating conveyors have as their greatest asset ehmination of explosion hazards. If pressurized air, water, or oil is available, they can be extremely practical since their drive design is relatively simple and pressure-control valves can be used to vaiy capacity either manually or automatically. 

To prevent surges, a well-trained operator would put the controller in manual mode and freeze the valve in an open position. This stops the control loop oscillations and decreases the compressor discharge resistance, thus breaking the surge cycle. Unfortunately, the operator has no way of knowing how much to open the valve and, subsequently, how much to close it. 

The PI controller, even when optimally tuned, is also unable to prevent surge. Furthermore, it is unable to stop surge once it occurs. In the above situation, the operator would correctly identify the problem as instability of the closed-loop PI controller. The only viable action would be to open the closed control loop by placing the controller in manual, thereby freezing the valve open. In this scenario, open-loop control will stop surge. 

If the control valve size is critical to the overpressure protection of the downstream equipment, and must not be increased, then this is clearly noted in all relevant documentation (specification sheets, flow diagram, operating manual, etc.,) and a warning notice plate is welded to the valve body. In such cases, an actual check of the valve installed or purchased should be made during the startup review. 

A process waste heat boiler was damaged when the control operator inadvertently closed the cooling water valve when he intended to open it. The manual control knob turned in the opposite direction from most of the other valves in the plant—the L, cooling water valve was air to close—most control valves were air... 

Bypass valves are sometimes installed to allow the control valve to be repaired without shutting in production. On large, important streams the bypass could be another control valve station. Manual bypass valves are... 

You can quickly identify these plant sections by reviewing process flow diagrams and valving arrangements. Isolation points are defined by control valves or powered block valves that can be remotely activated. Process hazard analysis techniques help you identify the maximum credible accident scenarios. (Note that manual valves should not be considered reliable isolation points unless they are located to be accessible following a major accident. However, remotely-activated valves can only be considered reliable isolation points if there are adequate reliability engineering and maintenance programs in place.)... 

In one plant, the operating procedures required that valve A should be placed into the "manual closed position." The process worker misinterpreted this information and instead of placing the valve controller in the manual position, he closed the block valve manually and deprived the plant of an essential feed. 

Directional control valves are designed to direct the flow of fluid, at the desired time, to the point in a fluid power system where it will do work. The driving of a ram back and forth in its cylinder is an example of when a directional control valve is used. Various other terms are used to identify directional valves, such as selector valve, transfer valve, and control valve. This manual will use the term directional control valve to identify these valves. 

Directional control valves may be operated by differences in pressure acting on opposite sides of the valve elements or may be positioned manually, mechanically, or electrically. Often two or more methods of operating the same valve will be used in different phases of its action. 

Control valves, both manual and automatic, used to regulate flow. 

Control valves for deluge Manual fire protection Separate units Place shutoffs well away from process areas. Install hydrants, monitors, and deluge systems. Add good drainage. Separate (space) plants on a site, and separate units within plants. Provide access from two sides. 

All fixed fire suppression system control valves should be located out of the fire hazard area but still within reach of manual activation. For high hazard areas (such as offshore facilities), dual feeds to fire suppression systems should be considered from opposite areas. For onshore facilities, firewater isolation valve handles should not be contained within a valve pit or a below grade enclosure within the vicinity of hydrocarbon process facilities, since heavy process vapors travel from the process and may settle inside. 

Also located in the control room is the manual-automatic switching hardware (or software). During start-up or under abnormal conditions, the plant operator may want to be able to set the position of the control valve himself instead of having the controller position it. A switch is usually provided on the control panel or in the computer system as sketched in Fig. 7.2. In the manual position the operator can stroke the valve by changing a knob (a pressure regula-... 

Vapor depressuring valves may be electric motor-operated gate valves, pneumatically operated control valves, or manually operated valves. Pneumatically operated valves should open on air failure, with provision to maintain pressure... 

Control valves, including all automatic and manual-actuating devices, should be tested at regular intervals. 

The extraction vessel outlet valve can be controlled either manually from the control unit or automatically by the phase boundary detector unit. The operation of this detector is based on the difference in refractive index between the organic and aqueous phases, and has been described elsewhere [34]. 

The only way the operator could restore the water level was to reverse this process. He manually restricted the flow of cold BFW through the level-control valve. This raised the stripper pressure, and stopped the flooding. 

Figure 3.5. Vacuum control with steam jet ejectors and with mechanical vacuum pumps, (a) Air bleed on PC. The steam and water rates are hand set. The air bleed can be made as small as desired. This can be used only if air is not harmful to the process. Air bleed also can be used with mechanical vacuum pumps, (b) Both the steam and water supplies are on automatic control. This achieves the minimum cost of utilities, but the valves and controls are relatively expensive, (c) Throttling of process gas flow. The valve is larger and more expensive even than the vapor valve of case (a). Butterfly valves are suitable. This method also is suitable with mechanical vacuum pumps, (d) No direct pressure control. Settings of manual control valves for the utilities with guidance from pressure indicator PI. Commonly used where the greatest vacuum attainable with the existing equipment is desired.

Valve outlet connection standardized by the Compressed Gas Association (CGA) (see ref. S). Corrosion of the manual control valve is indicated by sticking on opening and closing, in which case the valve is taken apart and cleaned. 

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