Remote actuated valve

Problem A safety instrumented function uses three analog transmitters as process sensors, a safety PLC and two remote actuated valves interfaced to the PLC with 24 VDC three way solenoids. What portion of the safety PLC is used in this safety instrumented function ... 

In the process industries the most common final element is a remote actuated valve. This assembly usually consists of a pneumatic/hydraulic control assembly, an actuator and a valve (Figure 11-1). The control assembly may be as simple as a three-way solenoid, a smart partial valve stroke box or a complex electro-pneumatic assembly with solenoids, test switches, pneumatic booster relays and quick exhaust valves. 

Remote actuated valves must be chosen to match process requirements. Design decisions include materials of construction, valve seat material, valve t q)e, actuator type and controls characteristics. The design must match utility supply levels (air pressure, hydraulic pressure, flow capacity) and tolerances with actuator design to provide the correct torque/thrust to the valve. The torque/thrust must be above breakaway requirements and must be below stress limits of the drive train. With some valves, the ratio of these values may limit the available operating safety factor. 

Table 11-2. Remote Actuated Valve Failure Modes and Diagnostic Techniques...

There are several different types of "partial valve stroke testing" that have been discussed under a common name. The simplest approach involves a system where the digital output of a PLC is momentarily de-energized in a remote actuated valve that is energized in normal operation. The PLC monitors a switch moimted to detect that the valve assembly has moved as a result of the momentary off pulse. 

To minimise personnel exposure from valve operations, motor operated, air operated or other remotely actuated valves are used where justified by activity levels and frequency of use. Where manual valves are used, either valve extenders or shielding is provided such that personnel need not enter a radiation area for valve operation. 

Install flame arresters on atmospheric vents to prevent fire on the outside of the tank from propagating back into the vapor space inside the tank. Provide fire resistant insulation for critical vessels, piping, outlet valves on tanks, valve actuators, instruments lines, and key electrical facilities. Provide remote controlled, automatic, and fire-actuated valves to stop loss of tank contents during an emergency provide fire protection to these valves. Valves should be close-coupled to the tank, and must be resistant to corrosion or other deleterious effects of spilled fluids. Vessels should be provided with overpressure relief protection. 

Each of these steps might be performed either by direct action of operations or emergency response personnel or by automatic systems. An example of the latter might be an array of toxic or flammable gas detectors that might trip an emergency shutdown system that closes remotely actuated block valves and vents off the process pressure to a flare if two adjacent sensors read above a predetermined vapor concentration. 

The inventory of contained liquid and gas can be calculated between isolation points to determine the amount of material that can be released for pro-cess-related scenarios. The time frame to close manual valves—depending on accessibility, operating conditions, and availability of personnel—is typically 10-30 minutes. For remotely operated valves actuated from the control room, 60-90 seconds is used for isolation. The release rate will decrease based on the pressure decay of the system once the system has been isolated. 

Manual stations—Local and remote manual trip stations should be readily accessible and conspicuously labeled. The number of trip stations will depend on the hazards present, size of the system, and personnel escape routes. All operating personnel should be trained on the location and use of these manual trip stations. Some facilities have only remote valves that can be manually opened without remote actuators not all systems have deluge valves. 

At least one remote manual actuation device independent of the manual actuation device located at the system actuation valve should be installed for all automatic water spray systems. 

Isolation or emergency shutdown (ESD) valves should be installed to stop fuel flow and the process feed flow into the heater in the event of heater tube rupture. These valves can be automatically actuated by controls or safety interlocks or can be manually operated remotely. Remote actuation can be from a control room console or in the field field actuation stations should be located at least 50 ft (15 m) from the heater. It is also common to provide a manual block valve, located at least 50 ft (15 m) from the heater, on each of the fuel and process feed lines. These should be accessible to operators in the event of an incident involving the heater. 

Where unloading of flammable liquids must be done from the bottom of the tank car or tank truck, a remote actuated unloading valve equipped with a fusible link for detecting high temperature should be provided. 

The catalyst preparation area is positioned between the two polyethylene production units with 60 feet separating each one. The aluminum alkyls storage canopy and isopentane horizontal storage tank are located at a remote area at an approximate distance of 250 feet away from the production and utility areas. The isopentane is transported to the catalyst preparation area through a 3-inch pipeline. A remote actuated isolation valve on this supply line that fails closed is located at the isopentane storage tank. This control valve and an associated isopentane feed pump are managed by the operator in the control room. 

It should be possible to easily isolate fluids in equipment and piping when potentially dangerous situations occur. This can be done using emergency block valves (EBVs). An EBV is a manually or remotely actuated protective device that should be used to provide manual or remote shutoff of uncontrolled gas or liquid flow releases. EBVs can be used to isolate a vessel or other equipment, or an entire unit operation. Manual valves are often used on piping at block limits where it is unlikely that there would be a hazard to personnel if an accident occurs. Remotely controlled EBVs are recommended on tanks and on piping in areas where it may be hazardous for personnel in the case of an accident, or where a quick response may be necessary. 

It should be possible to easily isolate fluids in equipment and piping when potentially dangerous situations occur. This can be done using emergency block valves (EBVs). An EBV is a manual or remotely-actuated protective device that should be used to provide manual or remote shut-off of... 

Will remote or self-actuating valves be installed where necessary ... 

In addition to the normal manual valve between a compressor and the common discharge header, there should be a fail-closed remotely actuated globe control valve with Monel trim and an equal percentage flow characteristic (HV-65 on Fig. 11.26). It should handle the full capacity of the compressor with a pressure drop of about lOkPa. When, during startup, the pressure instrument referred to above shows that the compressed gas pressure is equal to the discharge header pressure, the operator can open this valve slowly. 

Several dampers are operable in Cold Standby. The remote position of operable dampers ts indicated on the ventilation panel (480.30) in the CCR. Operable danqiers are remote actuated from the ventilation panel. Some pneumatic dampers have been plac in the required standby position.. The associated recover tanks were emptied and the air suppty lines (both compressed air and standby air systems) have been valved out or capped to nunimize the leakage potential in the operable portions of the compressed air system. 

The sophistication of the supervisory control system depends somewhat on the level of plant automation. In principle, all valves on the plant could be remotely actuated, allowing almost all procedures including start-up and shut-down to be "run" by the computer. In practice, such levels of automation are not cost-effective and a compromise is normally reached on the level of plant automation. 

In contrast to pressure regulators that control pressure, cylinder valves control flow. Manual or remotely actuated operators (integral or attached to the valves) are used to open and close the valves. 

In particular, remotely controlled valves that use pneumatic, hydrauUc, or electrical actuators are subject to actuator failure. In many cases, these... 

Leak Duratioa The Department of Transporation (1980) LNG Federal Safety Standards specified a 10-min leak duration other studies (Rijnmond Public Authority, 1982) have used 3 min if there is a leak detection system combined with remotely actuated isolation valves. Other analysts use a shorter duration. Actual release duration may depend on the detection and reaction time for automatic isolation devices and response time of the operators for manual isolation. The rate of valve closure in longer pipes can influence the response time. Due to the water hammer effect, designers may limit the rate of closure in liquid pipelines. 

Actuators. The problem of radiation damage to hydraulic fluids, elastomers, or electrical insulations is avoided by utilizing pneumatically powered metallic bellotvs for remote actuation of the valves. The actuator is a simple linear device which can be controlled with standard pneumatic controllers or regulators. The bellows may also be stacked to multiply the forces available. In the HRE 2, pneumatic actuators develop up to 5440 lb force. 

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