1.1 Reservoir

Reservoir or hydraulic fluid tank or oil tank is used to store the working fluid. The quality andcondition of working fluid is most important for satisfactory operation of system. Hence reservoiris designed, made and assembled with all necessary accessories to keep working fluid in bestoperating condition.A reservoir serves following functions: -1) To store sufficient quantity of working fluid.2) To dissipate heat of fluid.3) With the help of accessories it keeps fluid in best operating condition.

Types of reservoir: -There are two types of reservoir.1) Integral reservoir.2) Separate reservoirTank top Assembly type Reservoir: -

This is a rectangular tank. Width of tank is almost equal to height of tank, and length isapproximately double the width. Special feature of this type is, motor, pump, manifoldblock and most of the hydraulic valves and accessories are mounted on top cover of reservoir.Main advantage of this type of reservoir is its compactness. Disadvantage of this type is thatwhen oil immersed type of pump is used with bell-housing and vertical motor, then for any servicing of pump, oil of tank is to be drained out. And if tank is of large capacity such as 500 to 1000 litersthen storing such large amount of oil in another container is very difficult. One of the way by whichthis problem is solved, is by making top cover from thick steel plate, and for any servicing completetop cover is lifted along with motor, pump assembly mounted on it by over-head crane, and aftercompleting servicing and maintenance, tank top cover is again placed on it’s original position.

1.2 Filler Breather

Filler breather assembly is combination of two units, that is filler and breather, and it is usedto fill fluid in tank, and to filter air which is sucked in tank, when oil level drops in tank.Filler could be an independent assembly or combined with breather assembly. Filler is basically acoarse filter, which only avoids large pieces of cloths or other particle entering in tank while filling thefluid. But it is not fool proof system of complete filtering of fluid. Fluid should be separately filtered byfiltering unit, and then pump in reservoir. Filler is only an opening with some precaution. Independentfiller when not combined with breather, and when not in use, is plugged completely. It does not allowany liquid to pass in reservoir.Breather is also a coarse filter with approximately 40 micron mesh size filtering. It filtersair, which is sucked in tank. When it is combined with filler, we get compact filler breatherassembly. Breather is also available separately. Following sketch will explain the constructionof filler breather assembly.

1.3 Fluid Level Indicator

If hydraulic pump runs dry ( without oil) even for few minutes, then because of friction internalcomponents of pump get over heated, get sieged, and gets permanently damaged. Hence bymistake also system should not run dry. Oil level falls below suction level of pump due to leakagein pipeline, actuating very large size of cylinder for the first time, and natural evaporation of oil etc.Such fall of oil level happen even without the knowledge of operator. Hence to safe guard pumpagainst any human error, and against running dry, fluid level controller is used.Fluid level controller is a simple electric switch, which gets actuated when fluidlevel fall bellow particular level. The actuation and sensing of level may be by mechanicalor by electromagnetic means. Various manufacturers makes different types of fluid levelcontroller. Visit their Website, to study more details about fluid level controller.

1.4 Temperature Indicator

Optimum temperature range of hydraulic fluid is 40°c to 50°c. Above this range life of oilreduces. Hence temperature indicators are used to check the oil temperature regularly. Thereare three type of temperature indicator. First is simple thermometer, which is fixed in oillevel indicator, hence oil level as well as temperature could be viewed any-time.Second type is dial type indicator. This unit has a probe or sensor, which is immersed influid, and dial indicators are similar to pressure gauge, and temperature is indicated througha pointer.The third and most widely used type is Electronic Temperature indicator cum controller.This unit has a thermocouple type sensor which is immersed in oil, and electrically connected to an electronic controlling unit with LCD display. This unit indicate as well control the temperature by either switching off the main motor, or by actuating a cooling device.

1.5 Float switch

A float switch is a device used to detect the level of liquid within a tank. The switch may be used in a pump, an indicator, an alarm, or other devices. Float switches range from small to large and may be as simple as a mercury switch inside a hinged float or as complex as a series of optical or conductance sensors producing discrete outputs as the liquid reaches many different levels within the tank. Perhaps the most common type of float switch is simply a float raising a rod that actuates a micro switch.A very common application is in sump pumps and condensate pumps where the switch detects the rising level of liquid in the sump or tank and energizes an electrical pump which then pumps liquid out until the level of the liquid has been substantially reduced, at which point the pump is switched off again. Float switches are often adjustable and can include substantial hysteresis. That is, the switch's "turn on" point may be much higher than the "shut off" point. This minimizes the on-off cycling of the associated pump.

Some float switches contain a two-stage switch. As liquid rises to the trigger point of the first stage, the associated pump is activated. If the liquid continues to rise (perhaps because the pump has failed or its discharge is blocked), the second stage will be triggered. This stage may switch off the source of the liquid being pumped; trigger an alarm, or both.

1.6 Return Line Filter

If on suction side of pump, a filter with too fine mesh size is used, then pump may not beable to suck oil through fine mesh and cavitation may occur. Hence either immediatelyafter pump, or at exhaust line, filters with fine mesh sizes are used to clean oil.A return line filter consists of a paper filter cartridge, and a by-pass valve, assembled togetherin a aluminium body. The construction of paper filter cartridge is similar to diesel or oil filter used inautomobile engine. Check valve or by-pass valve, by-passes oil to system, when paper filter getschocked. By doing so, it saves the aluminium body of filter against permanent damage. It may alsohave a pressure gauge type of indicator. As paper filter element starts chocking, it increases backpressure. This back pressure is indicated by pressure gauge. The amount of back pressure indicatesthe extent of filter chocking.Filters at exhaust line are more common, and economical. Filter with 10 micron and25 micron filtrations are more commonly available in industry.

1.7 Suction Strainer

There is always possibility of small as well as large contamination in fluid. Hencea filter always should be provided on suction side of a pump. A coarse filter, which I providedat suction side of pump is called suction strainer.In industry a range of suction strainer are available from 5LPM to 450LPM capacity.Generally they are connected by threading, and available from ½ to 2" BSP threads sizes.Suction strainers are usually made of bronze, steel or stainless steel screening of 30to150 mesh size. They are pleated to increase surface area and wrapped around a perforatedsteel cylinder, as explained in following diagram.

1.8 Hydraulic vane pump

Hydraulic pumps are used in hydraulic drive systems and can be hydrostatic or hydrodynamic. A hydraulic pump is a mechanical source of power that converts mechanical power into hydraulic energy (hydrostatic energy i.e. flow, pressure). It generates flow with enough power to overcome pressure induced by the load at the pump outlet. When a hydraulic pump operates, it creates a vacuum at the pump inlet, which forces liquid from the reservoir into the inlet line to the pump and by mechanical action delivers this liquid to the pump outlet and forces it into the hydraulic system. Hydrostatic pumps are positive displacement pumps while hydrodynamic pumps can be fixed displacement pumps, in which the displacement (flow through the pump per rotation of the pump) cannot be adjusted, or variable displacement pumps, which have a more complicated construction that allows the displacement to be adjusted. Although, hydrodynamic pumps are more frequent in day to day life. Hydrostatics pump which are of various types works on the principle of Pascal's law. It states that the increase in pressure at one point of the enclosed liquid in equilibrium of rest is transmitted equally to all other points of the liquid, unless the effect of gravity is neglected. (in case of statics)

The simplest vane pump is a circular rotor rotating inside of a larger circular cavity. The centers of these two circles are offset, causing eccentricity. Vanes are allowed to slide into and out of the rotor and seal on all edges, creating vane chambers that do the pumping work. On the intake side of the pump, the vane chambers are increasing in volume. These increasing volume vane chambers are filled with fluid forced in by the inlet pressure. Inlet pressure is actually the pressure from the system being pumped, often just the atmosphere. On the discharge side of the pump, the vane chambers are decreasing in volume, forcing fluid out of the pump. The action of the vane drives out the same volume of fluid with each rotation. Multistage rotary vane vacuum pumps can attain pressures as low as 10−6mbar

1.9 Bell-Housing

There are two ways of fixing a pump to a motor. First by mounting motor and pump on acommon flat base plate. Motor has its build-in foots, if pump is of foot mounted type then it isadjusted to the centre line of motor and bolted to base plate. Or if pump does not have build-infoot but flange mounted, then a bracket is made, and then pump is mounted on bracket andcoupled to motor, as shown in following diagram.This arrangement requires large floor area, and it is too difficult to align the centre line of pump with centreline of motor. Misalignment results in damage ofbearing of both motor and pump and fast wear and tearof coupling. Second and most widely used alternative of fixingpump with motor is by means of bell housing as shownin following sketch.Bell housing is casted or fabricated structure, andaccurately machined. Motor mounted on one side andpump on other side. As it is accurately machined, henceit ensures perfect alignment of motor and pumpassembly.

1.10 Check valve

A check valve, clack valve, non-return valve or one-way valve is a valve that normally allows fluid (liquid or gas) to flow through it in only one direction. Check valves are two-port valves, meaning they have two openings in the body, one for fluid to enter and the other for fluid to leave. There are various types of check valves used in a wide variety of applications. Check valves are often part of common household items. Although they are available in a wide range of sizes and costs, check valves generally are very small, simple, or inexpensive. Check valves work automatically and most are not controlled by a person or any external control; accordingly, most do not have any valve handle or stem. The bodies (external shells) of most check valves are made of plastic or metal.

An important concept in check valves is the cracking pressure which is the minimum upstream pressure at which the valve will operate. Typically the check valve is designed for and can therefore be specified for a specific cracking pressure. Heart valves are essentially inlet and outlet check valves for the heart ventricles , since the ventricles act as pumps.

A ball check valve is a check valve in which the closing member, the movable part to block the flow, is a spherical ball. In some ball check valves, the ball is spring-loaded to help keep it shut. For those designs without a spring, reverse flow is required to move the ball toward the seat and create a seal. The interior surface of the main seats of ball check valves are more or less conically-tapered to guide the ball into the seat and form a positive seal when stopping reverse flow.

Ball check valves are often very small, simple, and cheap. They are commonly used in liquid or gel minipump dispenser spigots, spray devices, some rubber bulbs for pumping air, etc., manual air pumps and some other pumps, and refillable dispensing syringes. Although the balls are most often made of metal, they can be made of other materials, or in some specialized cases out of artificial ruby. High pressure HPLC pumps and similar applications commonly use small inlet and outlet ball check valves with both balls and seats made of artificial ruby, for both hardness and chemical resistance. After prolonged use, such check valves can eventually wear out or the seat can develop a crack, requiring replacement. Therefore, such valves are made to be replaceable, sometimes placed in a small plastic body tightly-fitted inside a metal fitting which can withstand high pressure and which is screwed into the pump head.

There are similar check valves where the disc is not a ball, but some other shape, such as a poppet energized by a spring. Ball check valves should not be confused with ball valves, which is a different type of valve in which a ball acts as a controllable rotor to stop or direct flow.

A diaphragm check valve uses a flexing rubber diaphragm positioned to create a normally-closed valve. Pressure on the upstream side must be greater than the pressure on the downstream side by a certain amount, known as the pressure differential, for the check valve to open allowing flow. Once positive pressure stops, the diaphragm automatically flexes back

to its original closed position. A swing check valve or tilting disc check valve is check valve in which the disc, the movable part to block the flow, swings on a hinge or trunnion, either onto the seat to block reverse flow or off the seat to allow forward flow. The seat opening cross-section may be perpendicular to the centerline between the two ports or at an angle. Although swing check valves can come in various sizes, large check valves are often swing check valves. The flapper valve in a flush-toilet mechanism is an example of this type of valve. Tank pressure holding it closed is overcome by manual lift of the flapper. It then remains open until the tank drains and the flapper falls due to gravity. Another variation of this mechanism is the clapper valve, used in applications such firefighting and fire life safety systems. A hinged gate only remains open in the inflowing direction. The clapper valve often also has a spring that keeps the gate shut when there is no forward pressure. Another example is the backwater valve (for sanitary drainage system) that protects against flooding caused by return flow of sewage waters. Such risk occurs most often in sanitary drainage systems connected to combined sewerage systems and in rainwater drainage systems. It may be caused by intense rainfall, thaw or flood.

A stop-check valve is a check valve with override control to stop flow regardless of flow direction or pressure. In addition to closing in response to backflow or insufficient forward pressure (normal check-valve behavior), it can also be deliberately shut by an external mechanism, thereby preventing any flow regardless of forward pressure.

A lift-check valve is a check valve in which the disc, sometimes called a lift, can be lifted up off its seat by higher pressure of inlet or upstream fluid to allow flow to the outlet or downstream side. A guide keeps motion of the disc on a vertical line, so the valve can later reseat properly. When the pressure is no longer higher, gravity or higher downstream pressure will cause the disc to lower onto its seat, shutting the valve to stop reverse flow.

An in-line check valve is a check valve similar to the lift check valve. However, this valve generally has a spring that will 'lift' when there is pressure on the upstream side of the valve. The pressure needed on the upstream side of the valve to overcome the spring tension is called the 'cracking pressure'. When the pressure going through the valve goes below the cracking pressure, the spring will close the valve to prevent back-flow in the process. A duckbill valve is a check valve in which flow proceeds through a soft tube that protrudes into the downstream side. Back-pressure collapses this tube, cutting off flow.

1.11 Relief Valve

The relief valve (RV) is a type of valve used to control or limit the pressure in a system or vessel which can build up for a process upset, instrument or equipment failure, or fire.

The pressure is relieved by allowing the pressurized fluid to flow from an auxiliary passage out of the system. The relief valve is designed or set to open at a predetermined set pressure to protect pressure vessels and other equipment from being subjected to pressures that exceed their design limits. When the set pressure is exceeded, the relief valve becomes the "path of least resistance" as the valve is forced open and a portion of the fluid is diverted through the auxiliary route. The diverted fluid (liquid, gas or liquid–gas mixture) is usually routed through a piping system known as a flare header or relief header to a central, elevated gas flare where it is usually burned and the resulting combustion gases are released to the atmosphere.[1] As the fluid is diverted, the pressure inside the vessel will stop rising. Once it reaches the valve's reseating pressure, the valve will close. The blowdown is usually stated as a percentage of set pressure and refers to how much the pressure needs to drop before the valve reseats. The blowdown can vary from roughly 2–20%, and some valves have adjustable blowdowns.

In high-pressure gas systems, it is recommended that the outlet of the relief valve is in the open air. In systems where the outlet is connected to piping, the opening of a relief valve will give a pressure build up in the piping system downstream of the relief valve. This often means that the relief valve will not re-seat once the set pressure is reached. For these systems often so called "differential" relief valves are used. This means that the pressure is only working on an area that is much smaller than the openings area of the valve. If the valve is opened the pressure has to decrease enormously before the valve closes and also the outlet pressure of the valve can easily keep the valve open. Another consideration is that if other relief valves are connected to the outlet pipe system, they may open as the pressure in exhaust pipe system increases. This may cause undesired operation.

In some cases, a so-called bypass valve acts as a relief valve by being used to return all or part of the fluid discharged by a pump or gas compressor back to either a storage reservoir or the inlet of the pump or gas compressor. This is done to protect the pump or gas compressor and any associated equipment from excessive pressure. The bypass valve and bypass path can be internal (an integral part of the pump or compressor) or external (installed as a component in the fluid path). Many fire engines have such relief valves to prevent the over pressurization of fire hoses.

In other cases, equipment must be protected against being subjected to an internal vacuum (i.e., low pressure) that is lower than the equipment can withstand. In such cases, vacuum relief valves are used to open at a predetermined low pressure limit and to admit air or an inert gas into the equipment so as control the amount of vacuum.

1.12 Shutoff Valve

When this type of valve is tripped, the flow is quickly stopped and an indicator disc tells the operator that the electrical circuit has been opened by a failure somewhere in the system. When the system failure has been corrected so that the circuit is again closed, the valve can be opened by the action of the hand lever. If, however, the system failure has not been satisfactorily corrected, the circuit will remain open and moving the hand lever will not open the valve, because the valve stem remains disengaged from the handle.

In a solenoid-operated safety shutoff valve, a spring action closes the valve instantly when an electric current fails and the solenoid ceases to be energized. The solenoid circuit is generally arranged so that it is broken upon failure of any element of the system. This valve cannot be re-opened until the solenoid is again energized. A safety shutoff valve should be fail-safe, that is close upon failure of any element of the input control system (such as temperature controllers, steam pressure controllers), air pressure, fuel pressure, current from a flame detector, or current from other safety devices such as low water cutoff, and high pressure cutoff.

However, sudden closing of a valve in a piping system may lead to water hammer or implosion so in special cases there may be additional items connected to the shutoff valve, such as a pressure relief valve or an aerator valve.

The coil of the valve solenoid must be connected in series with all of the elements. For this to operate, fuel, air and steam pressure can be converted to electrical signals by means of bellows, a bourdon tube, or a diaphragm-operated mercury switch.

1.13 Pressure Line Filter

Some of the hydraulic valves such as servo-valves, proportional valves etc. are madetoo precisely. They are very costly and too sensitive to contamination.To avoid any possibility of dust particle damaging the valves, less than 10-micron filters areused. Because of fine mesh size, some pressure is required to pass fluid through such fine filters. Ifthey are used at suction line, then cavitation may occur. If they are used at exhaust line, then aconstant backpressure will be created in system. Hence to avoid these two problems, these finefilters are fitted just after the pump, and before valves. Pressure line filter withstands the full workingpressure of system.The pressure line filter assembly after certain use starts clogging or choking due toaccumulation of contamination on the surface of filtering element. As choking increases,the pressure required to pass fluid through these filters also increases. Hence all the filterssuch as in line suction filters return line filters, and pressure line filters have some means toindicate the extent of choking. It may be a rotating colour disc or a pressure gauge likeindicator. And all the filters also have a simple type of relief valve. After choking, if filter elementsare not cleaned or replaced, then instead of building-up pressure, fluid start by-passing filter throughthese relief valves. This saves the permanent damage to the filter body, but contaminated fluid starts circulating in systemwithout filtration, whichmay damage the wholesystem.

1.14 Pressure Gauge

Pressure gauge is used to read the pressure of hydraulic system. A faulty gauge maymisguide while setting machine and excessive pressure setting may damage the system.Hence a good quality pressure gauge is too important in hydraulic system. Following factsshould be remembered while using pressure gauge.Pressure gauge should be very near to pump. As and when oil passes through valvespressure drops. If oil passes through more numbers of valves, pressure drop may be excessive(say 15 to 20 kg/cm2). Hence if pressure observed at the actuator end, and then setting ofpressure relief valve adjusted to get the required pressure, then pump has to develop 15 to 20kg/cm2 more pressure than the relief valve setting, to compensate for pressure drop.Pressure gauge commercially used in industry, uses “bourdon tube principle”. Bourdontube is a curved pipe which when pressurized tries to straighten. One end of this curved pipeis fixed, and connected to pressure line, other end which is blind, is free to move as pressureapplied. This movement, through ratchet and gear arrangement converted into rotary motion ofpointer.Bourdon tube is made from elastic material, hence after release of pressure it returnsto its original position. But when it is over pressurized beyond its elastic limit, then itundergoes plastic deformation, and do not return to its initial position. Hence pointeralso does not return to zero or initial position.All manufacturers claim that their pressure gauges can work up to maximum indicating capacity of their pressure gauge. But most of the time pressure gauge pointer does not return to zero

position, after taking pressure up to its maximum capacity. Hence always use pressure gauge of double the more capacity than working pressure. That means, for200kg/cm2 working pressure use pressure gauge of 400 kg/cm2 capacity.

1.15 Pressure Switch

A pressure switch is a mechanical device which converts a pressure change into an electricalfunction. The pressure change might be measured as pressure, vacuum, or differential betweentwo pressures input..Pressure switch uses diaphragm, piston, or other pressureresponsive sensor, coupled to the mechanical means to actuate aelectrical switch.A spool type of pressure switch consist of a valve body, a spool,spring and adjusting screw, assembled together as per followingdiagram.Pressure to be sensed act against spring force. As pressure increases, it over-comes the spring force, and pushes the piston onone side. This cause actuation of electrical switch.