basic hydraulic systems
TRANSCRIPT
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BASIC HYDRAULIC SYSTEMSSAFETY AND HYDRAULIC TRAINING UNIT
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ObjectivesUpon completion of this lesson, the student will: 1. State the work area safety practices. 2. Locate and identify the components of the hydraulic training unit. 3. Operate the basic hydraulic training unit.
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Basic Safety ProceduresIt is important that safety procedures are followed when working in the lab, in the shop or other work area. Practice the following procedures until they become habits. In any work area, you must: 1. Wear safety glasses or goggles at all times. 2. ALWAYS turn off the training unit before making or breaking connections with the components. 3. ALWAYS wipe your hands completely before touching electrical equipment, including the solenoid valve and the switch controlling the training unit. 4. Keep all body parts and loose objects away from operating cylinders. 5. If you are not sure about the operation of a circuit, consult your instructor before turning on the pump. 6. DO NOT clean hoses or plastic parts with chemical cleaning fluids.
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UNIT 2 Hydraulic Fundamentals Hydraulic Principles
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Objectives Upon completion of this lesson, the student will be able to: 1. State why liquid is used in hydraulic systems. 2. Identify Pascal's Law as applied to hydraulic principles. 3. State the characteristics of oil flow through an orifice. 4. Demonstrate an understanding of the basic hydraulic principles.
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Using a liquid There are several advantages for using a liquid. 1. Liquids conforms to the shape of the container. 2. Liquids are practically incompressible. 3. Liquids apply pressure in all directions.
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Practically incompresssable
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Gas is compressable
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Pascals Law
"Pressure exerted on a confined liquid is transmitted undiminished in all directions and acts with equal force on all equal areas."
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Pascals Law
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Mechanical advantage
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Orifice effect
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Blocked flow
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Restrictions in series
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Restrictions in parallel As the check valve in circuit one is set at 30 psi it will open first and give oil flow priority to circuit one. Circuit three will not receive oil flow until system pressure reaches 90 psi.
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Complete Quiz 2.1.1
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Unit 3
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Lesson 1
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Objectives Upon completion of this unit, the students will be able to: 1. State how basic hydraulic principles are used in the operation of hydraulic system components. 2. State the function of hydraulic tanks, fluids, pumps and motors, various valves and cylinders. 3. Identify the different hydraulic tanks, pumps and motors, fluids, valves and cylinders. 4. Identify the ISO symbol for the hydraulic tank, the pump and/or motor, the various valves and the cylinders.
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Hydraulic tank
The main function of the hydraulic oil tank is to store oil. The tank also removes heat and air from the oil. Tanks must have sufficient strength, adequate capacity and keep dirt out. Hydraulic tanks are
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Pressurised tank
The pressurized tank is completely sealed. Atmospheric pressure does not effect the pressure in the tank. However, when the oil is sent through the system, it absorbs heat and expands. The expanding oil compresses the air in the tank. The compressed air forces the oil out of the tank and into the system.
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Vented tank
The vented or un-pressurized tank differs from the pressurized tank in that the vented tank has a breather. The breather allows air to enter and exit freely. Atmospheric pressure on the top of the oil forces the oil out of the tank and into the system. The breather has a screen that prevents dirt from entering the tank.
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ISO schematic symbol
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Complete quiz 3.1.1
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Lesson 2
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Objectives Upon completion of this lesson the student will: 1. State the functions of hydraulic fluids. 2. Measure the viscosity of fluids. 3. State the meaning of viscosity index. 4. List the types of fire resistant hydraulic fluids.
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Function of hydraulic fluid Fluids are virtually incompressible. Therefore, fluids can transmit power instantaneously in a hydraulic system. The primary functions of hydraulic fluids are: Power transmission Lubrication Sealing Cooling
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Viscosity Viscosity is the measurement of a fluid's resistance to flow at a specific temperature. A fluid which flows easily has a low viscosity. A fluid which does not flow easily has a high viscosity.
A fluid's viscosity is affected by temperature. When a fluid becomes warmer, the fluid's viscosity becomes lower.
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The most common tool of measuring viscosity is the Saybolt The Saybolt Viscosimeter was invented by and named after George Saybolt.
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Petroleum productsAll petroleum oil becomes thin as the temperature goes up and thickens as the temperature goes down. If the viscosity is too low, there may be excessive leakage past seals and from joints. If the viscosity is too high, sluggish operation may be the results and extra power is needed to push the oil through the system. Viscosity of petroleum oil is expressed by the Society of Automotive Engineers (SAE) numbers: 5W, 10W, 20W, 30W, 40W, etc. The lower the number, the better the oil will flow at low temperatures.
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Synthetic oils Synthetic oils are formed by processes which chemically react materials of a specific composition to produce a compound with planned and predictable properties. Synthetic oils are specifically blended for extreme service at both high and low temperatures.
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Fire resistant fluids There are three basic types of fire resistant fluids: water-glycols, water-oil emulsions and synthetics.
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Water-glycols Water-glycol fluids contains 35% to 50% water (water inhibits burning), glycol (synthetic chemical similar to some anti-freeze) and a water thickener. Additives are added to improve lubrication and to prevent rust, corrosion and foaming. Water-glycol fluids are heavier than oil and may cause pump cavitation at high speeds. These fluids may react with certain metals and seals and cannot be used with some types of paints.
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Water oil emulsion Water-oil emulsion are the least expensive of the fire resistant fluids. A similar amount (40%) of water is used as in water-glycol fluids to inhibit burning. Water-oil can be used in typical hydraulic oil systems. Additive may be added to prevent rust and foaming.
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Synthetic oils Certain conditions may require that synthetic fluids be used to meet specific requirements. The fire resistive synthetic fluids are less flammable than oil and more suitable for used in areas of high pressure and high temperature. Many times fire resistant fluids react to polyurethane seals and may require that special seals be used.
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Oil life The hydraulic oil never wears out. The use of filters to remove solid particles and some chemicals add to the useful life of the oil. However, eventually the oil will become so contaminated that it will have to be replaced. In construction machines, the oil is replaced at regular time intervals.
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Complete quiz 3.2.1
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Lesson 3
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Objectives Upon completion of this lesson, the student will be able to: 1. State the differences between non-positive and positive displacement pumps; 2. State the differences between fixed displacement and variable displacement pumps; 3. State the operation of different types of pumps; 4. State the similarity and differences between pumps and motors; and 5. State how pumps are rated.
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Hydraulic pump
The hydraulic pump transfers mechanical energy into hydraulic energy. It is a device that takes energy from one source (i.e. engine, electric motor, etc.) and transfers that energy into a hydraulic form. The pump takes oil from a storage container (i.e. tank) and pushes it into a hydraulic system as flow.
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Pumps Pumps produce only the flow (i.e. gallons per minute, liters per minute, cubic centimeters per revolution, etc.) used in the hydraulic system. Pumps DO NOT produce or cause "pressure". Pressure is caused by the resistance to the flow. Resistance can be caused by flow through hoses, orifices, fittings, cylinders, motors, or anything in the system that hinders free flow to the tank. Pumps can be classified into two types: Non-positive displacement and positive displacement.
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Hydraulic motor
The hydraulic motor transfers hydraulic energy into mechanical energy. It uses the oil flow being pushed into the hydraulic system by a pump and transfers it into a rotary motion to drive another device (i.e. final drives, differential, transmission, wheel, fan, another pump, etc.).
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Non-positive displacement pumps
Non-positive displacement pumps have more clearances between the moving and stationary parts than positive displacement pumps. The extra clearance allows more oil to be pushed back between the parts as the outlet pressure (resistance to flow) increases.
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Positive displacement pumps There are three basic types of positive displacement pumps: gear, vane and piston. Positive displacement pumps have much smaller clearances between components. This reduces leakage and provides a much higher efficiency when used in a high pressure hydraulic system.
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Volumetric efficiency As pressure increases, the close clearances between the parts in a positive displacement pump do not produce the same output flow as input flow. Some oil will be forced back through the clearances between the high pressure chamber and the low pressure chamber. The resultant output flow, when compared to the input flow, is called "volumetric efficiency". Volumetric efficiency @ 1000 psi =
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Fixed displacement v variable displacement
The output flow of a fixed displacement pump is only changed by varying the speed of the pump rotation. It must be rotated faster to increase the flow or rotated slower to decrease the flow. The gear type pump is a fixed displacement pump. The vane type and piston type pumps may be fixed or variable. The output flow from a variable displacement pump may be increased or decreased independent of the speed of rotation. The output flow may be manual controlled, automatic controlled or a combination of manual and automatic controlled.
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Gear pump operation
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Pressure plates
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Vane pump operation
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Vane pumps
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Vane operation
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Pressure plates
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Balanced vane pump
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Variable vane pump Variable output vane pumps are controlled by shifting a round ring back and forth in relation to the rotor centerline. Variable output vane pumps are seldom, if ever, used in mobile hydraulic applications.
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Piston pumps
Most piston pumps and motors have similar or common parts and use the same nomenclature. The pump parts in Figure 3.3.17 are the head (1), the housing (2), the shaft (3), the pistons (4), the port plate (5), the barrel (6) and the
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Fixed v Variable
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Internal gear pump
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Gerotor pump
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Pump ISO symbols
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Motor ISO symbols
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Complete quiz 3.3.1
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Lesson 4
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Objectives Upon completion of this lesson the student will: 1. List the four most common pressure control valves. 2. State the functions of the relief valve, sequence valve, pressure reducing valve and the pressure differential valve. 3. Identify the ISO symbol for the four most common pressure control valves.
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Relief valves
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Pilot operated relief valve
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Relief valve ISO symbol
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Variable ISO relief valve symbol
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Sequence valve
The sequence valve (Figure 3.4.8) is simply a pilot operated relief valve in series with the second circuit. The sequence valve is use when two circuits are supplied by one pump and one circuit has priority over the other.
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Sequence valve ISO symbol
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Pressure reducing valve The pressure reducing valve allows two circuits of different pressures to be supplied by the same pump. The maximum supply oil pressure is controlled by the system relief valve. The pressure reducing valve controls the maximum pressure in the controlled oil circuit.
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Pressure reducing valve
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Pressure reducing valve ISO symbol
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Pressure differential valve
The pressure differential valve maintains a specified difference in pressure between two circuits.
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Pressure differential ISO symbol
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Complete quiz 3.4.1 3.4.2 3.4.3
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Lesson 5
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Objectives Upon completion of this lesson the student will: 1. State the function of the manual spool type control valve, the rotary type control valve and the solenoid actuated control valve. 2. State the function of the simple check valve, the pilot operated check valve and the shuttle valve 3. Identify the ISO symbols for the various directional control valves.
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Directional control valve
The directional control valve is use to direct the supply oil to the actuator in a hydraulic system.
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Open Center Directional Control Valve in HOLD Position
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Open Center Directional Control Valve in RAISE Position
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ISO directional control valve symbols
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ISO Ports
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3 position valve
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Directional control valve actuators
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Three Position, Six Way, Open Center, Manual Controlled Valve
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Rotary valves
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Check valve
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Pilot operated check valve
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Check valve ISO symbols
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Make-up valve
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Solenoid actuators
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Solenoid actuated directional control valve
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Solenoid actuated ISO control valve
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Complete quiz 3.5.1
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Lesson 6
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Objectives Upon completion of this lesson the student will: 1. State the function of the orifice, the needle valve, the flow control valve, the pressure compensated flow control valve, and the quickdrop valves. 2. Identify the ISO symbols for the various flow control valves.
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Orifice An orifice is a small opening in the oil flow path. Flow through an orifice is affected by several factors. Three of the most common are: 1. The temperature of the oil. 2. The size of the orifice. 3. The pressure differential across the orifice.
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Variable orifice
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Pressure differential
Flow through an orifice is affected by the pressure differential across the orifice. The greater the pressure differential across the orifice, the greater the flow through the orifice. In Figure 3.6.5, pressure differential is illustrated using the two tubes of tooth paste. When the tube of toothpaste is gently squeezed as in A, the pressure difference between the inside of the tube and the outside of the tube is small. Therefore, only a small amount of tooth paste is forced out. When the tube is squeezed with greater force as in B, the pressure difference between the inside of the tube and the outside of the tube increases and a larger
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Pressure compensated flow control valve
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Quick drop valve
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Flow control ISO symbols
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Complete quiz 3.6.1
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Lesson 7
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Objectives Upon completion of this lesson the student will: 1. Identify the two basic types of hydraulic cylinders. 2. State the function of the two basic types of hydraulic cylinders. 3. Identify the basic cylinder components.
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Single acting cylinders
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Double acting cylinders
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Effective area of a cylinder
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Cylinder seals
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Snubbers (Dampers)
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Complete quiz 3.7.1 Practical exercises pump and valve operation. In the hydraulics test room. 3.3.1 3.3.2 3.3.3 3.4.1 3.4.2 3.4.2 3.4.4 3.5.1 3.5.2 3.5.3
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Unit 4
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Objectives Upon completion of this unit, the student will: 1. Trace the oil flow from the tank to the pump, through the various hydraulic components, and back to the tank. 2. State the function of each component in the system. 3. State the system operation in the various modes.
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Hydraulic colours Green Tank oil or oil connected to the tank. Blue Blocked oil Red High pressure oil or pump oil Red and White Stripe High pressure oil but less than Red oil. Orange Pilot pressure oil
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Lesson 1
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928G wheel loader hold position
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Pilot control valve
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Metering stem
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Main control valve
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Main control valve
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Combination valve
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Control valve (lower)
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Control valve float
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