RESERVOIR:
The tank which stores the working medium (oil) and supplies to pump and also takes back the return and drain oil in a hydraulic system and protects the medium from external contamination is called Reservoir. It also allows the oil to cool through its walls and allows contaminants to settle and air to separate. Generally in many cases it houses cooler, return filters, air breather( a device which allows air to move in and out of acontainer to maintain atmospheric pressure), level indicator, level switches (float switches).
SUCTION LINE:
The pipe line connecting tank to pump generally with a shut off valve in between is called suction line. Without opening this valve, pump should not be started. Generally a hose or rubber bellows is provided in this line to isolate the vibrations of the pump.PUMP:
The element which transfers oil/fluid from one point to another point or which gives flow is called pump. Pump only gives flow, but the resistance to flow develops pressure. In hydraulics only positive displacement pumps are used. In these pumps there is positive sealing between suction and delivery. For every revolution of pump, a fixed amount of oil is transferred from suction to delivery irrespective of load conditions.
Practically there will be minor internal leakages which are negligible. This fixed amount of oil transferred is called Displacement of pump. The displacement when multiplied by speed of the electric motor driving the pump, gives Discharge of the pump (flow of the pump) Centrifugal pumps (non positive displacement type) are not used in hydraulic systems. In this if delivery is closed, pressure will not build up beyond a particular limit. Safety valve is not required. Most commonly used positive displacement pumps used in hydraulics are
Gear, piston and vane types are popular. A positive displacement pump should never be started without opening the suction valve. There should be sufficient oil level in tank so that air does not enter the pump. If air enters the pump, it will run with high noise and it will be damaged very soon. This is called aeration. Even though sufficient oil is there,aeration can occur due to any loose pipe joints in suction line. Pump is always followed by a relief valve (safety valve), pressure gauge, check valve and shut off valve.
CHECK VALVE/NON-RETURN VALVE:
It is a valve which allows flow in one direction only. Generally provided after the pump in most of the cases to take care of reverse rotation of pump. It is also used in many places of the circuit as a bypass etc. Check
valve and non-return valve are same.
PRESSURE GAUGE:
It is provided to know the pressure and for setting of variousvalves, pressure switches.
SAFETY VALVE/ RELIEF VALVE:
Both are same and it is the most important component of Hydraulic system. It limits the maximum pressure in the system so that elements, hoses, cylinders, pipes etc does not burst due to high pressure. I t also protectsthe equipment and system from over loading. When the system pressure increases beyond the set point, the safety valve opens and relieves the excess oil to tank.
ACCUMULATOR:
It is a reservoir of pressurized hydraulic fluid i.e. storage of energy by means of spring or compressed nitrogen, dead weight. It is basically a pressure vessel. No welding is allowed on this.1. Bladder type
2.Piston type
3.Dead
weight type
4. Direct gas loaded type.
Nitrogen is generally used in accumulators but never use oxygen as it may result in explosion. You should never open a pressure line with accumulator in line. Always isolate/preferably drain the accumulator before starting the job.Accumulator is used
(a) for smooth functioning of HS without pressure and flow fluctuations
(b) as an emergency power source for essential operations in case of power failure.
(c) for holding pressure for long times in a circuit (d) a big pump can be replaced by a small pump ( cost & energy saving) and many other purposes.
DIRECTION CONRTOL VALVES:
Distributor/Master valve / DC valve are all same. If a pump supplies oil directly to a cylinder, it is not possible or convenient to control the load or to change the direction of motion. Hence a dc valve is provided in between pump and the load cylinder to stop/start /reverse the motion of the load. DC valve can be activated by a lever, cam, solenoid, pedal, pneumatic/hydraulic pressure depending on the design and requirement. Most commonly used are solenoid operated and they are having two/ three positions. If you are using a two position valve you cannot stop the cylinder in between.
There are many varieties of dc valves.
FLOW CONTROL VALVES:
To control the speed of the actuator /load, the amount of oil flowing into the cylinder is controlled by means of these valves. Generally these are provided before the cylinder or in branch circuits where flow is to be controlled. Simple needle/globe valve can also be used as flow control valve in some cases.SEQUENCE VALVE:
In a simple punching machine, the job is held in position by a clamping cylinder at low pressure and then a hole is punched by another cylinder at a high pressure. Now these two cylinders are always to be operated in definite sequence only. This sequence can be achieved by electrical/mechanical or by hydraulic means through a valve called sequence valve. Hydraulic sequencing is most common and versatile. A dc valve supplies oil to cylinder-1 and through a sequence valve to cylinder -2. It is almost similar to a safety valve but not same.
PRESSURE REDUCING VALVE:
In some HS many cylinders are working at different pressures ,but a few cylinders does not require full pressure and can work at a low pressure .Then all these selected cylinders are supplied oil through a valve known as pressure reducing valve. In pressure reducing valve, the output pressure cannot go beyond a particular limit. This setting will be lower than the safety valve setting.FILTERS:
All hydraulic elements work under close tolerances and they are precision items with mirror surface finish.Contaminants and dust are the single largest enemy of the HS as they cause malfunctioning and jamming of valves and fast wear out of elements. The contaminants are internally generated in the system and some are external to the system. Working medium is to be regularly cleaned from these contaminants. Hence oil filters are used in suction line, pressure line and return line and before an important precision valve/pump as per the need. This will improve the performance of the system.The coarse filter used in suction line of pump sometimes is called STRAINER .Hydraulic systems are most reliable, if the contamination is kept under control, and breakdowns can be minimized. In a filter the hydraulic oil is allowed to pass through a porous medium (like clay, paper, wire mesh, synthetic fiber etc) so that the dust particles and other contaminants are retained and only clean oil goes ahead into the system.Offline filtration (mostly portable) systems are also used for up keeping the system depending on the criticality. Electrostatic Liquid cleaners are also used nowadays. These are very simple to operate and cheap.PRESSURE SWITCH:
The hydraulic oil under pressure pushes a small plunger which in turn makes/breaks an electrical contact. These are provided in the system for safety and efficient operation or for achieving a particular logic sequence. Contact Manometer is a pressure gauge with electrical contacts, which does almost the same job, but they are less reliable and less robust.
LEVEL SWITCHES:
Generally the reservoir is provided with low level and high level float switches, so that they give alarm of low oil level/ high level and can be used for interlocking purpose. Float switch operates due to buoyancy in oil. Generally the low level switch is interlocked with the drive of pump, so that when there is no oil due to any reason, the pump will trip or will not allow the pump to start.ACTUATORS:
Generally the hydraulic cylinders and hydraulic motors are called actuators. These actuators do the actual job of lifting/lowering/pushing/rotating /holdingetc . Hydraulic motor replaces many applications of electric motors due to many advantages like speed control, over load protection etc. Hydraulic motors are almost similar to pumps. When these are supplied oil at pressure, they will give rotary output. Generally gear/vane/piston motors are in use.Generally two types of Hydraulic cylinders are commonly used viz,
a) Double acting cylinders, which can be used for pulling and pushing ,consists of piston , piston rod, body covers, seals and fasteners, eye . Basically a sealed piston with rod reciprocates inside a cylindrical body under the pressure of oil..
B) Single acting cylinder.
These types can only push/lift a load. The single acting cylinder cannot retract due to hydraulic force. It retracts due to weight/spring/ load. Hydraulic jacks are generally single acting type.
SEALS:
The component which prevents the motion of the fluid in the undesired direction is called seal/packing. Can also be defined as that component that separates two fluids. The functions of the seal area) to seal the hydraulic fluid in a closed chamber
b) Maintains pressure
c)stops dirt/water/contamination from entering the system
d) separates two
fluids
e) performs any combination of the above functions.
In simple terms a seal stops internal or external leakages. Cost of the seal is a small fraction, but determines the efficiency of the system. Problems associated with seals: Wastage of fluid leaked, fire hazards, slippery floor,makes equipment and products dirty, environment pollution, depleting natural resources.Leather, cork, ropes are the oldest seals, which are widely used in the earlier days. Then natural rubbers, synthetic rubber , PTFE, Polyurethane, POM etc are used nowadays. Seals should be handled delicately, and sharp tools should not be used.
PIPES, FITTINGS, CLAMPS:
Generally pickled, flushed seamless pipes are used in hydraulic systems. For maintenance convenience and ease of laying, pipe joints are provided at suitable places. For small pipes union joints are used and in bigger pipes flange joints are used. There is large variety of pipe joints of different standards and designs areavailable. Care should be taken that different fittings do not get mixed up. Also while doing maintenance on fittings thread type/seat design/size etc should be matched. Otherwise lot of problems will result. Pipes should be properly clamped and supported; otherwise the joints get loosened during working due to vibrations. Pipe clamps are made of wood/ Aluminium/ synthetic materials. Wooden clamps are to be avoided due to environment protection. Aluminium clamps are used where high temperatures are there. Synthetic clamps are commonly used nowadays. While laying hose pipes, the layout should be
smooth, and they should not crisscross/twist/entangle and rub each other.