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Working principle of rotary vane steeringgear. Draw

Rotary Vane Gear

These consist of two elements:

1. a cylindrical static casing (stator) with usually three internal vanes which projectradially inwards

2. a rotor keyed to and concentric with the rudder stock, the rotor has rotor vaneswhich project radially outwards into the spaces formed by the stator vanes.

The spaces formed between the stator and rotor vanes are used as high and low pressurechambers. The main advantage of the system is that it is compact, occupying about 1 / 10the space of a ram system. The disadvantages are ;

1. it has a long oil sealing path2. it is a constant torque machine at all angles of helm compared to the ram system

where due to the Rapson slide effect, the torque available increases withincreasing helm.

Where 100% redundancy is required two rotary vanes in piggy back are used.

All vanes are spheroidal graphite cast iron secured to the cast iron rotor and stator by high tensilesteel dowel pins and cap screws. Rotor strength is maintained by keys fitted full length of therotary vane. Steel sealing strips are fitted along the working faces, backed by synthetic rubber ingrooves along the working faces which are elastically loaded, so as to ensure that contact withthe mating surfaces is maintained in order to hold the hydraulic pressures.

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Rotation of the stator is prevented by means of two anchor brackets and two anchor bolts . Theanchor brackets are securely bolted to the stool and vertical clearance is arranged between theinside of the Stator flanges and the top and bottom of the anchor brackets to allow for verticalmovement of the rudder stock. This clearance varies with each size of rotary unit but could beabout 40 mm total . It is essential that the rudder carrier should be capable of restricting thevertical movements of the rudder stock to less than this amount.

The anchor bolts are fitted with special bushes in halves, shaped externally in order to pre-loadthe synthetic rubber shock absorbers , which are fitted between them and the anchor brackets.The maximum deflection of the shock absorbers under full load is approximately 1 mm.

The working angle of the gear is governed by the number of vanes and their thickness. Vanes actas rudder stops when a moving vane contacts a fixed vane. Valves at inlet to the chambers may

be shut causing a hydraulic lock. In the rotary vane units the Mechanical Advantage is unity atall angles and hence torque is constant

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Torque = p.a.n.r.where n = number of rotating vanes

a. Describe the procedure for opening a bottom end bearing for inspection makingreference to the positioning of the crank and the safety precautions to be observed.

(6)b. State how the bearing clearance may be checked and adjusted when necessary. (4)c. State TWO defects which may be encountered during inspection of the bottom end

bearing and crankpin giving possible causes of EACH. (4)d. State TWO checks which should be made before returning the engine to service

following overhaul of the bottom end bearing. (2)

a.

Engine shut down and secured. Turning gear engaged, cocks open Carry out risk assessment.

Check all lifting gear and tools within certification & free from defects. Permit to work obtained (crankcase an enclosed space). Clearance to turn engine obtained from bridge. Check that no one working elsewhere on engine or on or over shafting.

Turn engine to TDC Mount a chain block either side of the

crankcase Screw eye bolts into threaded holes on

either side of lower bearing half. Attach chain blocks, wire strops, and

Fit four guide shoe retaining blocks in tothe crosshead guides. This will preventthe crosshead and con rod from movingdown the engine when it is turned.

Wrap a strop around the bottom of thecon rod and attach to a chain block

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take up slack. Remove locking plates and slacken

bearing stud nuts using hydraulic jacks Remove jacks and nuts. Using chain blocks lower the bearing

cover, taking care not to damage thethreads of the studs or the crankpin journal.

Remove the bearing cover from thecrankcase.

mounted on the side of the engine

Turn the engine while pulling the thelower part of the con rod with the liftingtackle so that the crankpin turns out ofthe top half of the bearing. Take carethat the crankpin does not foul on thetop edge of the bearing.

The crankshaft can be turned to bottomdead centre and the top half of the

bearing examined / removed.

b.

To check the bottom end bearing clearance.

Turn the engine to BDC. Isolate the turning gear. Climb down into crankpit and measure the clearance using feelers.

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The clearance is measured on the bottom halfof the bearing because the mass of the runninggear acting downwards means that the top half

of the bearing is sitting on the journal. On alarge engine (960mm bore) this clearance can be 0.8mm

With modern shell bearings, the clearance is manufactured into the shells. When the clearancehas reached a maximum as laid down in the instruction manual the bearing is changed.

Thick wall shell bearings fitted on some engines have the clearance adjusted by fitting shims between the bearing halves. The shims are of equal thickness on both sides of the bearing

housing.

c.

When inspecting the pin check for ovality. This is caused by the varying downward load on thecon rod in both the power and compression stroke. If the ovality is more than 25% of the

bearing clearance then there is a danger of the hydrodynamic lubrication being affected.

Check the top bearing shell for evidence of the bearing material separating from the steel shell backing. This is caused by the high pressure oil supply from the crosshead acting on the back ofthe shell and deforming it. Shows by cracking of the white metal.

d.

Two checks before returning the engine to service following overhaul of bottom end:

Oil flow through bearings; Start pump and ensure oil is reaching bottom end and flowingout of bearing sides.

Engine turns through at least one revolution with turning gear whilst observing ammeterfor signs of excessive current.

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The sketch illustrates a modern two stroke bottom end arrangement. A forged steel con rodcomplete with bottom end bearing housing has replaced the older style con rod with marine

palm and separate bearing. The bottom half of the white metal bearing can either be cast intothe cap or, like the top half, be a separate steel backed shell. With modern steel backed shell

bearings, the clearance is built in and non adjustable; when it becomes excessive the bearing ischanged. Older thick walled bearings used shims to adjust the clearance. Because the load onthe con rod is always downwards on a two stroke engine, it is the top half of the bearing whichtakes the load. Oil is supplied down from the crosshead, through a bore in the con rod andround the outside of the top shell to the ends of the bearing half where it is fed into the bearingthrough two holes. The bottom half of the bearing may have a groove cut into it to assist incarrying the oil around.

Studs screwed into the bottom half of the bearing cap have replaced the older style through bolts. When removing the bottom end cap, care must be taken not to damage the crankpin.Because of the varying load on the crankpin, it has a tendency to wear oval; this should bechecked as excessive ovality (25% of clearance) can affect hydrodynamic lubrication.Distortion of the bearing top half due to downward oil pressure from the crosshead has beenknown to separate the white metal from the steel backing.

b.

The varying load on the 2 stroke bottom end on the power and compression stroke is alwaysdownwards. The bottom end bolts are stretched when tightening the nuts using hydraulic jacks

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and are under tension. This tensile stress remains constant during the operation of the engine.

On a four stroke engine, the bottom end bolts are again under tension. However, the inertialoads due to the mass of the reciprocating parts cause a stress reversal in the connecting rod from high compressive stress (during power and compression stroke) to a low tensile stress

between the exhaust and inlet strokes. This stress reversal in the con rod is reflected in the bottom end bolts where the tensile stress in the bolts is now not constant. This cyclic stressingmeans that bottom end bolts on a 4 stroke engine have a limited life, approx 12 - 15000 hrs. To

prevent cracks starting, the bolts themselves are undercut at the bottom of the thread, changes insection have smooth radiuses and the finish is good with no blemishes.

D'carb Process Of Auxiliary Generators Explained In Detail

Carrying out complete decarb of a marine generator is a normal routine. Learn about the entire

process here.

Introduction

D'carb of auxiliary engine is nothing but the carrying out of certain routines at intervals prescribed by the manufacturer or experience. Normally the following should be done during amarine decarb to free the engine from anomalies

o Every 3000hrs take out cylinder head , take the worn out mountings and/or over haul themountings

o All units cylinder head, piston, connecting rod , and turbocharger to be overhauledo

Clean sump tank and fill with fresh lube oilo Take crank shaft deflection before and after removal of bearingso What ever actions taken should be recorded in the maintenance record book

D'carb preparation1. Make sure the all stand by auxiliary engines are ready

2. Keep all the special tools and other tools ready3. Go through the previous records/manual for clearance and adjustments4. Put the display card "MEN AT WORK", "DON'T START"5. Close air bottle valve to auxiliary engine and engine start and stop valve6. See that the turning bar is not in the flywheel and should be in place7. Open the indicator cocks 8. If the main bearing is to be removed, check crank shaft deflections 9. Close lube oil, fuel oil, fresh water inlet/outlet valve, drain the cooling water line and remove

connections

Cylinder head of generator engine before cleaning

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Removal of cylinder head

1. Scavenge manifold , exhaust manifold rocker arm, lube oil drain connection from rockerarm, rocker arm tank and cover connection to be removed

2. Fuel oil high pressure connection from fuel pump to the injector, fuel valve coolingconnections in and out (either diesel or water) to be removed

3. Remove the rocker arm assembly and the push rod. Remove all the mountings such asstarting valve, indicator cock, relief valve and exhaust valve assembly

4. Remove the rocker cover and check any marking on cylinder head nuts and studs. If notorque spanner is available, note down the markings.

5. Open the cylinder head nut with box spanner and extension rod. Never use the torquespanner. With box spanner available note down the marking .

6. Put the cylinder head lifting tool and before lifting make sure all the connections areremoved. Also ensure that the liner is not removed along with the cylinder head

7. Take out the copper joint between the head and the liner

Piston removal pictures

Removal of piston and connecting rod

1. After lifting the head, check the liner surface for score marks, blow past etc. Crackremove the ridges or deposits if any on the top surface to avoid the lifting of liner alongwith the piston and breakage of piston rings while lifting piston

2. Open the crank case door and remove the bottom end bearing bolts after removing thelock arrangement and the remove the bolts

3. Remove the bottom half of the bottom end bearing

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4. Bring the piston to TDC. Make sure the bolt holes on the piston top, lifting tool holesmust be cleared from carbon deposits. Threads should also be checked and cleared

5. Put the piston lifting tools and tighten the bolts6. Lift the piston and remove top shell of bottom end bearing7. Place the piston on the piston stand and cover the crankcase pin to avoid the foreign

material damaging the crank-pin.

Cylinder liner and other parts d'carb

Cleaning the carbon content on all the parts of engine

1. Clean the piston rings, measure dimensions and keep them in order2. Clean the piston ring grooves thoroughly and measure the groove thickness at 3 different

points3. Check for the deposits on piston crown (Sulphur, carbon or thick vanadium deposits) and

measure the dimensions4. Remove the gudgeon pin and clean the gudgeon lube oil holes as well as the bush or

small end bearing5. Check the bolts of connection rod for any cracks6. Every 20,000 hrs engine connecting rod bolt must be replaced7. If new piston rings are going to be replaced, then there is no need for measurement8. Calibrate the liner thickness by using template

Assembly of the engine parts

1. First put the piston rings one by one and measure the butt clearance for all the rings2. Then measure the axial clearance between piston rings & grooves

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3. Place the piston guide on top of the liner and bring the particular crank shaft to TDC.Apply sufficient lube oil and start lowering the piston. Make sure that butt gap should not

be in line it may cause blow past4. Before engaging check the crankpin for any cracks or scratch5. Check the bottom end bearing clearance and if needed measure the main bearing

clearance as well6. Taper clearance is checked7. Check for any cracks in the water jacket and in the cylinder head8. Replace all rubber joints and copper gasket to be put on the cylinder cover9. Put the cylinder head gasket in the top of the cylinder10. Anti-seizure coating or powder like molycote, copper slip should be used. It is applied to

avoid any seizure mainly on the threads or joints and it will be easier while removal11. Tighten the cylinder mounting according to torque specified as in manual and make all

connection like lube oil, fuel, jacket cooling water connections etc12. Fit the rocker arm back

Starting of generator engineStarting of an engine from "stop" state is something which needs to be done with care, especiallyif the interval of starting is sufficiently long. The following is a checklist of all the checks whichideally need to be carried out before starting the generator. In actual practice sometimes theengineers might take some of these for granted and skip, but it is advisable not to indulge in sucha practice. Infact these checks are generic for any four stroke engine starting process

1. Check the turbocharger sump oil level, governor, alternator, forward and aft lube oillevels, and diesel oil level in service tank

2. Open the indicator cock

3. Prime the lube oil to all parts by hand pump or by motor driven priming pump4. Ensure that all jacket cooler valves, lube oil cooler valves, air cooler valves should be inopen position

5. With use of the Turning bar turn the fly wheel and check for any resistance on the bottomend bearing and check any water / fuel coming out through indicator cocks

6. While turning engine, check all visible lube oil points are lubricated7. Remove the turning bar from fly wheel and put in the place8. Drain the auxiliary air bottle9. Blow through engine (ie: by turning engine with air). In order to ensure that no water is

inside combustion chamber if it is present it may cause water hammering10. Close the indicator cocks and pull lever from stop to start

11. When the needle in RPM indicator deflects to some value of (0-25 rpm) put the lever inrun condition12. The engine will run on fuel oil once the generator picks up the rated speed13. Put generator on load by closing air circuit breaker14. For checking the alternator fore and aft bearing lube oil level by opening oil plug in the

alternator and the ring bearing while rotating splash lube oil from the sump can be seen15. In order to synchronize the incoming generator with running generator syncroscope

method/dark lamp method is used

http://www.brighthubengineering.com/marine-engines-machinery/41368-components-of-a-turbocharger/http://www.brighthubengineering.com/marine-engines-machinery/41368-components-of-a-turbocharger/http://www.brighthubengineering.com/marine-engines-machinery/41368-components-of-a-turbocharger/http://www.brighthubengineering.com/marine-engines-machinery/10205-what-is-an-indicator-diagram-in-context-of-marine-diesel-engines/http://www.brighthubengineering.com/marine-engines-machinery/10205-what-is-an-indicator-diagram-in-context-of-marine-diesel-engines/http://www.brighthubengineering.com/marine-engines-machinery/10205-what-is-an-indicator-diagram-in-context-of-marine-diesel-engines/http://www.brighthubengineering.com/marine-engines-machinery/31782-how-are-generators-synchronized-on-a-ship/http://www.brighthubengineering.com/marine-engines-machinery/31782-how-are-generators-synchronized-on-a-ship/http://www.brighthubengineering.com/marine-engines-machinery/31782-how-are-generators-synchronized-on-a-ship/http://www.brighthubengineering.com/marine-engines-machinery/31782-how-are-generators-synchronized-on-a-ship/http://www.brighthubengineering.com/marine-engines-machinery/10205-what-is-an-indicator-diagram-in-context-of-marine-diesel-engines/http://www.brighthubengineering.com/marine-engines-machinery/41368-components-of-a-turbocharger/

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est and Overhaul of Fuel Injection Valveswritten by: Chief Engineer Mo hit Sanguri edited by: Lamar Stonecypher updated: 10/18/2013

This article discusses the testing and the overhaul of fuel injectors of marine engines,the testingof the needle and guide condition of the fuel valve, and the procedure to overhaul and inspect theinjectors taken out of the marine diesel engines.

Fuel Valve Checks

The fuel valves taken out from the engine must be checked for function and performance. Evenin engines which are stopped on heavy fuel oil in ports the fuel injector taken out must beimmediately tested with diesel oil before they get cold as this will flush and clean thecomponents. It must be noted that if the fuel valves taken out are tested after they have cooled,will show bad performance even if they were performing satisfactorily in service.

In the majority of cases the fuel injectors have a good spray profile but they open up at a less pressure. The pressure adjustment can be done without opening up the valve and should be doneso. The engine manufacturers also instruct that unless the fuel injector valve has a major problemlike holes choked or valve dripping, they should not be opened up. The valve should be cleanedfrom the outside, pressure checked, pressure adjusted and tagged.

Inspection and Repairs

In the case where the fuel injector valve is not performing as required and has some defect, thenit needs to be opened up and overhauled. The assembly and the disassembly have to be done as

per the instructions given by the engine manufacturer. However, below is a general guide aboutwhat you will most likely have to do.

3 way ball valves

www.zmvalve.com/

3 way ball valves from China,quality assurance.

Cooling Water Treatment

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After the fuel valve has been disassembled then the following checks have to be done:

1. The needle guide should be immersed in clean diesel oil and the needle taken out and checkedfor free movement. In the case of any resistance which may be due to the presence of carbon orfuel sludge the needle may be put in and pulled out in succession many times while keeping itsubmerged in diesel oil. It is important to do this in a container full of clean diesel oil so thecontaminants can be flushed away.

2. After the needle guide has been cleaned, the needle should be taken almost out and then let itfall in with its own weight. A free and smooth movement with small jerks as the clearance ismaking way for the oil to come out is an indication that the clearances are all right and the needleguide is in good condition. It must be noted that the needle should fall fully into the seat.

3. On the other hand if the needle falls fully in one go, then the clearances have increased and thefuel will leak past the spindle and less fuel will go in the cylinder. The needle must be inspectedfor any wear marks if this happens. The needle guide can be used but must be changed soon.

4. If the needle does not go down and gets struck then it must be thoroughly cleaned again. Ifstill there is no improvement then the needle might have become bent. Check the needle for anysigns of overheating.

5. The push rod end should be checked for any abnormal wear.

6. The seating between the nozzle body and the valve body if damaged can be repaired bylapping with fine lapping paste. It must be noted that the lapping paste should be thoroughlyflushed away with clean diesel oil and thereafter blown dry with compressed air.

7. Check the nozzle spring for breakage, poor seating and other defects. Change if required.

8. Check the leak off pipes, shims, packing etc for the condition. If the fuel valve is water cooled,the cooling pockets should be cleaned with compressed air.

Tests and Adjustments

1. After the parts are cleaned and inspected the fuel valve is assembled as per the manufacturersinstructions and thereafter tested for function and performance.

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2. The assembled fuel valve is installed on the test stand and after purging the pipe line themanual handle is operated in quick succession. The nozzle should start discharging with a sharpcrackling noise at the set pressure. The pressure at which the injector is supposed to fire dependsupon the manufacturers engine design but normally is between 250 to 350 kg/cm2 with anallowance of plus or minus 10 kg/cm2.

3. In case the lifting pressure is not correct, it can be adjusted by the adjusting screw.

4. The spray characteristics should be satisfactory and as per the manufacturers advice.

5. All the holes of the injector should be firing and can be checked by a torch light or a filter paper can be folded as a cone and then the injector tested. The holes on the filter paper will showthe number of holes firing. In this procedure you must be careful as the high pressure spray canenter the skin and is toxic for us.

6. The spray angle should be as stated by the manufacturer. The atomization of the fuel should

take place and solid spray should not come out.

7. Clean diesel oil should be used for the testing purpose.

8. In the case that the fuel valve is dripping the needle guide should be taken out and repaired.

Caution

The needle and the guide is always a pair and should not be interchanged with another one.Cleanliness is the most important factor in making fuel valves. A clean fuel valve lasts a longertime. The fuel under pressure can enter the skin and the blood stream and is toxic for humans.

Take care that you stay away from the spray. The fine mist can catch fire and in inflammable. Donot smoke or use naked lights where the fuel injectors are being tested.

Construction of the Thermostatic Expansion Valveswritten by: Haresh Khemani edited by: Lamar Stonecypher updated: 8/20/2013

This articles describes all the parts of the thermostatic expansion valve and also their working.

Construction of the Thermostatic Expansion Valve

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Construction details of the internally equalized thermostatic expansion valve are shown in thefigure to the right. It is comprised of a metallic body which encloses the following parts:

1) Metallic Diaphragm: The metallic diaphragm is a flexible metallic plate that can expand dueto pressure of refrigerant inside the refrigeration or air conditioning plant.

2) Power Element: This is the upper portion of the thermostatic expansion valve which is filledwith gas. In the case of the air conditioning system, the gas filled in element is the same as thegas filled in the air conditioning system. For instance if the air conditioning system is has R22refrigerant, the gas filled in the power element is also R22. The power element is connected tothe feeler bulb, via thin tubing. The same gas is also filled in the tubing and the feeler bulb. Thusthe feeler bulb, the connecting tubing and the power element all form a single flexible chamber.

The feeler bulb is connected to the evaporator and senses the temperature inside the evaporatorof the refrigeration system. The volume of the gas inside the power element changes as per thetemperature sensed by the feeler bulb inside the evaporator. If the temperature inside theevaporator is high the gas in the feeler bulb will expand; the gas in power element will alsoexpand and its pressure will increase. The gas pressure inside the power element tends to open

the thermostatic expansion valve. Algae Harvesting

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3) Valve Seat and Needle: The valve seat and the needle are located in the lower side of the

thermostatic expansion valve. The valve seat is the metallic plate that provides passage for theflow of the refrigerant. The needle is connected to the lower part of the diaphragm and it movesinside the opening of the valve seat. When the diaphragm moves down due to high pressureinside the power element the needle also moves down thus opening the thermostatic expansionvalve and when the needle moves up the valve closes. The valve seat and the needle form theorifice that allows the flow of the refrigerant through it.

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4) Spring: The spring is located at the bottom of the thermostatic expansion valve. It is undercompression and tends to move the needle of the valve in an upward direction and close thevalve. The pressure of the spring is adjusted by the manufacturer and it depends on the degree ofsuperheat in the evaporator. You should purchase the TEV of the required spring pressure.Though there is a screw for changing the spring pressure, it is preferrable not to change its

setting unless you are sure that the plant is working satisfactorily.

5) Liquid Inlet Port and Outlet to Evaporator: The liquid inlet port is connected to the tubingcoming from the condenser. The refrigerant enters the thermostatic expansion valve via this port.After passing through the orifice of the valve seat and the needle the refrigerant leaves to theevaporator in flashed conditioned via outlet to the evaporator.

7) All refrigeration systems require equalization lines. For more information, see this source:http://www.swtc.edu/ag_power/air_conditioning/lecture/expansion_valve.htm

Working of the Thermostatic Expansion Valve

written by: Haresh Khemani edited by: Lamar Stonecypher updated: 2/16/2010

This article describes the working of commonly used thermostatic expansion valve or TEV. TEVis used as the throttling device in number of refrigeration and air conditioning plants of highercooling capacities.

Pressures Acting Inside the Thermostatic Expansion Valve or TEV

The working of the thermostatic expansion valve can be explained with the help of the attachedimage of the valve. The valve comprises of external body inside which various parts as shown inthe figure are enclosed.

There are three pressures acting inside the thermostatic expansion valve. P1 is the pressure at thetop of the thermostatic expansion valve acting inside the power element above the diaphragm.Due to this pressure the diaphragm tends to move down due which the needle also moves downand the valve tends to open. When the evaporator temperature becomes higher the gas in thefeeler bulb expands due to which the gas pressure inside the power element increases. Thiscauses the downward movement of the needle to open the valve

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The pressure P2 is the pressure acting on the lower side of the diaphragm due to the refrigerant pressure inside the evaporator. This pressure tends to move the diaphragm upwards and close theopening of the valve.

The pressure P3 is the spring pressure that tends to close the opening ofthe valve. This pressure remains constant.

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The pressures P2 and P3 act against the pressure P1. The pressure P1 tends to open the valvewhile the pressure P2 and P3 tend to close the thermostatic expansion valve. Thus if the valvehas to open P1 should be greater than combined forces of P2 and P3.

How Thermostatic Expansion Valve Works?During the normal working of the refrigeration plant the thermostatic expansion valve remainsopened in certain position. When the refrigeration load increases, the temperature inside theevaporator also increases. In such cases there is need of the more refrigerant to take care of theincreased load. The increased temperature in the evaporator is sensed by the feeler bulb of thethermostatic expansion valve. This leads to the expansion of the gas in the feeler bulb and also inthe power element of the TEV leading to the increase in pressure P1. Due to this the diaphragm

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of the TEV moves down and tends to open the valve further to increase the flow of therefrigerant to the evaporator.

At the same time the pressure P2 below the diaphragm also increases due to superheating of therefrigerant inside the evaporator. This pressure tends to close the valve. There is also spring

pressure P3 below the diaphragm that opposes the opening of the valve. If the increase in therefrigeration load is much higher the pressure P1 overcomes pressure P2 and P3 leading to thefurther opening of the thermostatic expansion valve. This allows for the increased flow of therefrigerant to the evaporator to take care of the extra load.

When the refrigeration load reduces, the magnitude of pressure P1 reduces and the combined pressures P2 and P3 overcome pressure P1 that allows for partial closing of the valve so the flowof the refrigerant to the evaporator reduces. Thus the TEV maintains the flow of the refrigerantinside the evaporator as per the refrigeration or air conditioning load. The TEV constantlymodulates the flow to maintain the superheat for which it has been adjusted by the spring.