Actuators hydraulic system

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. 

The energy within a hydraulic system is of no value until it is converted into work. Typically, this is accomplished by using an actuating device of some type. This actuating device may be a cylinder, which converts the hydraulic energy into linear mechanical force a hydraulic motor, that converts energy into rotational force or a variety of other actuators designed to provide specific work functions. 

A similar action takes place in a fluid power system in which the fluid takes the place of the projectile. For example, the pump in a hydraulic system imparts energy to the fluid, which overcomes the inertia of the fluid at rest and causes it to flow through the lines. The fluid flows against some type of actuator that is at rest. The fluid tends to continue flowing, overcomes the inertia of the actuator, and moves the actuator to do work. Friction uses up a portion of the energy as the fluid flows through the lines and components. 

Most hydraulic systems have built-in sources of air. Leaky seals in gas-pressurized accumulators and reservoirs can feed gas into a system faster than it can be removed, even with the best of maintenance. Another lesser-known but major source of air is air that is sucked into the system past actuator piston rod seals. This occurs when the piston rod that is stroked by some external means while the actuator itself is not pressurized. 

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. 

Flow control valves are used to regulate the flow of fluids. Control of flow in hydraulic systems is critical because the rate of movement of fluid-powered machines or actuators depends on the rate of flow of the pressurized fluid. 

Pilot Pressure Auxiliary pressure used to actuate or control hydraulic system components. 

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

An example of a smart material is one developed by Toyota. The multilayer piezoelectric ceramic inside an automobile shock absorber has about five layers for sensing road vibrations. The multilayer stacks positioned near each wheel of the auto also have about 100 layers that act as the actuator, all part of the same ceramic. After analyzing the vibrational signals, a voltage is fed back to the actuator stack, and a response occurs by pushing on the hydraulic system of the auto to cancel the vibration. 

Actuators can be classified as conventional and unconventional actuators. Conventional actuators are commonly used as essential components for mechatronic systems (see Pig. 1 (left)). These are, for instance, electrical motors, pneumatic actuators, hydraulic pistons, or relays. 

Electrically powered actuators have not historically been able to provide fail safe functionality. Today there are some smaller partial turn electric actuators that have a spring return in the event of total loss of power. While these have the ability to close without power, there is a significant addition of complication that impacts the reliability when compared to a simple spring return hydraulic or pneumatic actuator. A response to this has been the electro-hydrauUc actuator that permits the safety functionality of a hydraulic piston fail safe actuator. The electrical portion provides power to the hydraulic system and the loss of which may be treated as a trip signal in addition to the basic shutdown signal. 

The components of a hydraulic system are similar to those of the pneumatic system. Figure 11-14 shows the components of a hydraulic system. The pressure of the hydraulic fluid is provided by the system s pump. The hydraulic pump is a device that creates flow in the system. The reservoir stores the hydraulic fluid before it is pressurized by the pump. Transmission lines carry the pressurized hydraulic fluid to the control valve and actuators. The control valves regulate the flow and pressure of the hydraulic fluid. The actuators transfer the fluid power into mechanical power. 

Each mould carrier is usually provided with two pneumatic cylinders for opening and closing. Upon demand, the closing system can be actuated hydraulically or mechanically. 

Administrative control of the hydraulic shield doors provides a worker safety function by 1) precluding lowering of the Room 108/109 shield door (door 2A) while the Room 101/108 shield door (door 1) is down, and 2) precluding lowering of the Room 109/Zone 2A shield door (door 3A) with workers in the Zone 2A canyon, the Zone 2A airlock, or the north end of Room 112. Keyed locks in the shield door hydraulic system control panel prevent unintended actuation of the shield doors. 

It should have rehable instruments. All necessary auxihary equipment (dry compressed instrument quality air, UPS, pneumatic and hydraulic system for actuators, solenoid valves) should always be in well-maintained condition. 

A variety of devices are used to implement the power stage, depending on the actuator used to move the servo system. These range from small DC motors to larger AC motors and even more powerful hydraulic systems. This section will briefly discuss the power stage options for the smaller, electric driven servo systems. 

Wolfe, C. Wendt, E. Application of ERF in Hydraulic Systems. Proc. AXON-VDI/E Actuator 94 Conf, Bremen (1994), pp. 284-287... 

Process technicians use hydraulic systems (see Figure 9-6) to open or close valves, lift heavy objects, run hydraulic motors, and stop the rotation of a rotary or reciprocating device. A hydraulic system is a collection of equipment designed to apply pressure on a confined liquid in order to perform work. A similar process is used in the brake systems of most cars and trucks. A hydraulic system is composed of a fluid reservoir, strainer, pump, piping, flow control valve, pressure control valve, four-way directional control valve, and actuator (cylinder, piston). 

The reflector drive mechanism consists of a hydraulic system that operates at the reactor start-up and shutdown and a ball screw system that connects a reflector to the motor that is actuated during normal operation (Figure XV-10). The mechanism has six driving systems corresponding to the six azimuthally separated reflectors. The six ball screw systems are fixed on a platform supported by the hydraulic system. For a reactor shutdown, the hydraulic pressure is released by opening scram valves to move the reflectors downward. The mechanical part of the reactor shutdown system has redundancy in that the platform is divided and the scram valves are set in parallel. 

In the consideration of seals or O rings for the aircraft industry, it is worth knowing the basic fluid flow mechanism in the hydraulic system, since the purpose of seals in aircraft is to preserve the pressure in such a system. Every aircraft hydraulic system has two major parts, the power section and the actuating section. The power section provides fluid flow, regulates and limits pressure. 

What function does an actuator serve in a hydraulic system ... 

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