Hydraulically operated actuator

Actuators for control valves come in three basic designs pneumatic, electric, and hydraulic. Pneumatic actuators, which convert air pressure to mechanical energy, use three designs diaphragm, piston, and vane. Electrically operated actuators convert electricity to mechanical energy. Common examples include solenoid valves and motor-driven actuators. Hydraulically operated actuators convert liquid pressure to mechanical energy. The hydraulic actuator uses a liquid-tight cylinder and piston to move or position the valve stem. 

Modern subsea trees, manifolds, (EH), etc., are commonly controlled via a complex Electro-Hydraulic System. Electricity is used to power the control system and to allow for communication or command signalling between surface and subsea. Signals sent back to surface will include, for example, subsea valve status and pressure/ temperature sensor outputs. Hydraulics are used to operate valves on the subsea facilities (e.g. subsea tree and manifold valves). The majority of the subsea valves are operated by hydraulically powered actuator units mounted on the valve bodies. 

Hydraulic power supply This actuates brakes and also feeds the yawing and pitch control (if they are also hydraulically operated). 

C, hydraulically operated (3600 bar, adopted from BASF), a Lower stem b, Gland c, Flexible coupling d, Upper stem e, Hand wheel f, Actuator g, Bushing h, Adjustment of the gland. 

The resulting opening can have sharp, chamfered, or rounded edges on the outside of the wall (Fig. 4.25 A-C). The inside, where the side core meets the main core, will always be sharp. This method is frequently used and is based on either cam-actuated or hydraulically operated slides which move the side core in and out of molding position. This motion can be at right angles to the center of the vertical axis of the product, or at any (reasonable) required angle, in which case the mold cost would increase even more. 

As most throttling control valves are still operated bv pneumatic actuators, the control-valve device descriptions that follow relate primarily to devices that are used with pneumatic actuators. The function of hydraulic and electrical coimteiparts are very similar. Specific details on a particular valve-control device are available from the vendor of the device. 

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. 

The hydraulic jar again uses a direct mechanical impact blow. The hydraulic fluid in this tool acts mainly to provide a delay while the desired derrick pull is achieved prior to actuation of the tool. Such tools may also be operated by compressed gas in a closed chamber. The compressed gas can be used to drive a hammer within the jar that strikes the top of a tool anvil. 

Water Water is a serious contaminant of hydraulic systems. Hydraulic fluids are adversely affected by dissolved, emulsified, or free water. Water contamination may result in the formation of ice, which impedes the operation of valves, actuators, and other moving parts. Water can also cause the formation of oxidation products and corrosion of metallic surfaces. 

A hydraulic system must have a reserve of fluid in addition to that contained in the pumps, actuators, pipes and other components of the system. This reserve fluid must be readily available to make up losses of fluid from the system, to make up for compression of fluid under pressure, and to compensate for the loss of volume as the fluid cools. This extra fluid is contained in a tank usually called a reservoir. A reservoir may sometimes be referred to as a sump tank, service tank, operating tank, supply tank or base tank. 

A valve is defined as any device by which the flow of fluid may be started, stopped, regulated or directed by a movable part that opens or obstmcts passage of the fluid. Valves must be able to accurately control fluid flow, system pressure and to sequence the operation of all actuators within a hydraulic system. 

Sequence valves control the sequence of operation between two branches in a hydraulic circuit. In other words, they enable one component within the system to automatically set another component into motion. An example of the use of a sequence valve is in an aircraft landing gear actuating system. 

Weschler et al. (1990) reported that the concentration of individual paraffins present in the air of a building was 0.0088-0.262 mg/m3 and was associated with operating a hydraulic elevator. Mineral oil hydraulic fluids, therefore, may be released to the air during use in hydraulic elevators (and probably other hydraulic equipment) and can come from volatilization or as mists or aerosols from fluid reservoirs and mechanisms such as actuation pistons. It is not likely that significant concentrations in air will occur from such sources. 

Four different types of tasks are performed by automation. Two involve the sequencing of valves and pumps Involved 1n the setup and completion of the designed experiment through the operation of the test and hydraulic fluid systems. The other tasks involve the control of the temperature bath and data collection. To perform these tasks, a1r-actuated solenoids and optically coupled sol Id-state relays are used. These devices are controlled by an electrical circuit consisting of the device connected 1n series with a power supply and a channel on the actuator card In the HP 3497. The power supply 1s either 24 VDC for use with the solenoids or 5 VDC for the solid-state relays. The actuator output channel acts as a simple on/off switch which allows power to be supplied to the solenoid or relay when closed. The logic of the circuit 1s controlled by application programs running on the local HP 1000. 

By themselves, valves cannot control a process. Manual valves require an operator to position them to control a process variable. Valves that must be operated remotely and automatically require special devices to move them. These devices are called actuators. Actuators may be pneumatic, hydraulic, or electric solenoids or motors. 

Pneumatic actuators are normally used to control processes requiring quick and accurate response, as they do not require a large amount of motive force. However, when a large amount of force is required to operate a valve (for example, the main steam system valves), hydraulic actuators are normally used. Although hydraulic actuators come in many designs, piston types are most common. 

The principles of operation of a hydraulic actuator are like those of the pneumatic actuator. Each uses some motive force to overcome spring force to move the valve. Also, hydraulic actuators can be designed to fail-open or fail-closed to provide a fail-safe feature. 

A major advantage of solenoid actuators is their quick operation. Also, they are much easier to install than pneumatic or hydraulic actuators. However, solenoid actuators have two disadvantages. First, they have only two positions fully open and fully closed. Second, they don t produce much force, so they usually only operate relatively small valves. 

Hydraulic actuators use fluid displacement to move a piston in a cylinder positioning the valve as needed for 0-100% fluid flow. This type actuator is incorporated when a large amount of force is necessary to operate the valve. 

Z) Walking Bearn Test. The purpose of this fuze test is to det the operating characteristics of pressure-actuated fuzes. The test consists of placing the test fuze under the end of a rod that is attached to the test equipment. A hydraulic hand pump, which is a part of the equipment is operated behind a barticade with the desired load being applied to the fuze (p IIB-40 of Ref 39)... 

Power actuated/assisted safety valves (CSPRS - controlled safety pressure relief system) A spring-operated safety valve actuated or assisted by an externally powered control device which can be hydraulic, pneumatic or electric (Figure 3.15). 

A CSPRS is, in fact, a spring-operated SRV which can operate as stand alone but in normal operations is controlled by an actuator (usually pneumatic or hydraulic) and which opens upon the signal of an instrumentation loop. Due to the additional force on the spring, more accurate set pressure can be... 

Solenoid Valves The electric solenoid valve has two output states. When sufficient electric current is supplied to the coil, an internal armature moves against a spring to an extreme position. This motion causes an attached pneumatic or hydraulic valve to operate. When current is removed, the spring returns the armature and the attached solenoid valve to the deenergized position. An intermediate pilot stage is sometimes used when additional force is required to operate the main solenoid valve. Generally, solenoid valves are used to pressurize or vent the actuator casing for on/off control valve application and safety shutdown applications. 

PMTC liquids are used in hydraulic actuators of membrane compressors and as operating liquids in hydraulic systems. 

Piston or ram type briquetting presses are operated as follows. The material to be briquetted is placed into a forming die which is closed on all but one side face. A close fitting ram or piston then enters into the die s open side and exerts the force required to produce the briquet. The briquet is then ejected or stripped out of the die. The ram or piston (which is also sometimes referred to as the stamp or punch) which enters into the die can be actuated either mechanically or hydraulically. A typical installation has the following characteristics ... 

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