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1. Safety devices on refrigeration system<\/strong> 2. What is critical temperature ?<\/strong> 3. What is the primary refrigerant ?<\/strong> 4. What is secondary refrigerant ?<\/strong> 5. What is solenoid valve? How to operate? Why fitted ?<\/strong> 6. What is the function of thermostatic expansion valve ?<\/strong> 7. What is relative humidity ?<\/strong> 8. What is saturated air ?<\/strong> 9. What is super heating ?<\/strong> 10. UNDER CHARGE Symptoms<\/strong> 11. OVER CHARGE<\/strong> 12. AIR IN THE SYSTEM<\/strong> 13. MOISTURE IN THE SYSTEM <\/strong><\/p>\n Symptoms<\/strong> 14. Cause of expansion valve chocking<\/strong> 15. OIL IN THE SYSTEM Symptoms<\/strong> Remedy<\/strong> Defective Suction valve <\/strong>Indication<\/strong> Defective Discharge valve <\/strong>Indication<\/strong> 16. How do take in action high pressure cut out and low pressure cut out ? H. P pressure cut out<\/strong> 17. Leakage Test for Refrigerant<\/strong> 18. What is refrigeration ?<\/strong> 19. What is air conditioning ?<\/strong> 20. What is ventilation ?<\/strong> 21. Comfort zone ?<\/strong> 22. Advantages of secondary refrigerant ?<\/strong> Reasons for defrosting<\/strong> 23. Defrosting methods ?<\/strong> Direct expansion grid system<\/strong> : Hot gas defrosting 24. Purpose of ventilation for cargo hold ?<\/strong> 25. What is short cycling ?<\/strong> 26. Why fitted high pressure cut out ?<\/strong> 27. Why fitted master solenoid valve for large plant ?<\/strong> 28. Explain about one method of refrigerant charging ?<\/strong> 29. Why super heat is required at evaporator outlet ?<\/strong> 30. How to fill fridge plant compressor oil ?<\/strong> 31. Types of expansion valve.<\/strong> 32. Prevention of Liquid Flow Back<\/strong> <\/p>\n","protected":false},"excerpt":{"rendered":" 1. Safety devices on refrigeration system 1) L. P cut-out on compressor suction side: Set at a pressure corresponding to 5\u00b0C below the lowest expected evaporating gauge reading 2) H.P cut-out on compressor discharge side: Set at a pressure corresponding to 5\u00b0C above the highest expected evaporating gauge reading 3) Lube oil low pressure cut-out: […]<\/p>\n","protected":false},"author":1,"featured_media":5888,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[79],"tags":[],"class_list":["post-5887","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-marine-engineering-competency-exams-study-blogs"],"_links":{"self":[{"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/posts\/5887","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/comments?post=5887"}],"version-history":[{"count":3,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/posts\/5887\/revisions"}],"predecessor-version":[{"id":5891,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/posts\/5887\/revisions\/5891"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/media\/5888"}],"wp:attachment":[{"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/media?parent=5887"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/categories?post=5887"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/seadonna.com\/blog\/wp-json\/wp\/v2\/tags?post=5887"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
\n1) L. P cut-out on compressor suction side: Set at a pressure corresponding to 5\u00b0C below the lowest expected evaporating gauge reading
\n2) H.P cut-out on compressor discharge side: Set at a pressure corresponding to 5\u00b0C above the highest expected evaporating gauge reading
\n3) Lube oil low pressure cut-out: Oil pressure usually set at 2 bar above crankcase pressure
\n4) Cooling water L .P cut-out in condenser side
\n5) Safety spring loaded liquid shock valve on compressor cylinder head
\n6) Bursting disc on cylinder head, between inlet and discharge manifold
\n7) Bursting disc on Condenser, [if fitted]
\n8) Relief valve on Condenser; air purging valve on condenser
\n9) Master solenoid valve: to prevent liquid being entered into Compressor, when the plant is standstill, especially in Large Plant<\/p>\n
\nCritical temperature above which it is impossible to liquefy the refrigerant regardless of pressure.
\nIt should be as high as possible and certainly above the maximum expected condenser temperature.<\/p>\n
\nIt is a medium which is used in a vapour compression cycle to remove heat from a low temperature region and convey it to a high temp: region .It undergoes change of physical state during its working cycles.
\n1) Mostly volatile liquid and employed inside direct expansion closed system.
\n2) Evaporate at low temperature and at reasonable pressure
\n3) Condense at SW temperature at reasonable pressure<\/p>\n
\nIt is a substance which transfers heat by conduction and convection. Brine is a secondary refrigerant .Its density 1250 kg \/m2
\n1) It is a non volatile liquid during it working cycle and employed at large, complex installation, to avoid circulation of expansive Primary Refrigerant in large quantities.
\n2) Cooled inside Refrigeration Machinery Room and pumped around the ship to batteries in each cargo space<\/p>\n
\n\udbc0\udc40 Solenoid valve is a liquid stop valve.
\n\udbc0\udc40 The valve is fully open and close.
\n\udbc0\udc40 To control the cool room temp: within set limit
\n\udbc0\udc40 It is a electro magnetic cut in cut out devices when the cool room temp reaches the desire point, the pressure switch which is connected to the thermo bulb in the cool room shut the solenoid valve which stop the refrigerant flow into the evaporator.<\/p>\n
\n1) To control the flow amount of liquid refrigerant to the evaporator in such a way as to keep practically the entire coils filled with the evaporating refrigerant.
\n2) To keep constant super heat on the refrigerant vapour leaving the evaporator.
\n3) It sudden drop in pressure and temperature
\n\udbc0\udc40 Automatic and prompt responds of refrigerant flow to match the Evaporator Load.
\n\udbc0\udc40 Prevention of Liquid Refrigerant being entered into the Compressor.
\n\udbc0\udc40 Maintaining appropriate amounts of Refrigerant in the High pressure side and Low pressure side of the system.<\/p>\n
\nRatio of amount of water vapour in given volume of air, to maximum amount of water vapour that can be present before precipitation occurs.
\nIt is the mass of water vapour per unit volume of air compared to the mass of water vapour per unit volume of saturated air at the same temperature.<\/p>\n
\nThe air contains maximum wt of water vapour at the particular temperature.<\/p>\n
\nTemperature above which the saturated temp:<\/p>\n
\n\udbc0\udc40 Low discharge pressure
\n\udbc0\udc40 Large bubbles in the liquid sight glass
\n\udbc0\udc40 Compressor delivery temp: high.
\n\udbc0\udc40 The machine runs for longer periods between cut out. Remedies
\n\udbc0\udc40 To charge the refrigerant until the bubbles disappears in the liquid sight glass and charging will correct the pressure gauge reading.
\n\udbc0\udc40 To find out the leaky points by halide torch or soap solution or electronic leak detector.<\/p>\n
\nSymptoms<\/strong>
\n\udbc0\udc40 It is indicated by high compressor discharge pressure.
\n\udbc0\udc40 Compressor runs cold.
\n\udbc0\udc40 Excess frost on compressor suction line after evaporator.
\n\udbc0\udc40 Full of sight glass.
\nRemedies<\/strong>
\nThe excess refrigerant is released to atmosphere through the purging valve fitted on the condenser until discharge pressure return to normal.<\/p>\n
\n. Symptoms<\/strong>
\n\udbc0\udc40 High condenser and compressor temp:
\n\udbc0\udc40 Abnormally high discharge pressure
\n\udbc0\udc40 Jerky pointer gauge
\n\udbc0\udc40 Very small bubbles in liquid sight glass.
\nRemedies<\/strong>
\nTo remove the air from the system \u2013
\n\udbc0\udc40 Change the compressor to manual position
\n\udbc0\udc40 Closed the liquid stop valve after the condenser
\n\udbc0\udc40 Pumping down the entire charge into the condenser
\n\udbc0\udc40 Until the suction pressure just above zero.
\n\udbc0\udc40 Stop the compressor and closed the consider inlet valve
\n\udbc0\udc40 Then allowed to cool the consider contents.
\n\udbc0\udc40 Air is expelled through the purging valve until the refrigerant gas appears at the valve.<\/p>\n
\n\udbc0\udc29 Starving of evaporator and rapid condenser pressure rise cause compressor short cycling.
\n\udbc0\udc29 Frost at expansion valve inlet. Remedy
\n\udbc0\udc29 Clean expansion valve filter.
\n\udbc0\udc29 Renew drying agents of dehydrator.<\/p>\n
\nWhen a valve is functioning correctly frost forms on the outlet side of the valve, and if the inlet side does show frosting then this is a sign of blockage.
\n\udbc0\udc29 It is caused by dirt or freeze up by water present in the system.
\n\udbc0\udc29 Starving of evaporator and rapid consider pressure rise cause compressor short cycling.
\nRemedy<\/strong>
\n\udbc0\udc29 Clean the expansion valve filter
\n\udbc0\udc29 Renew the drying agent of dehydrator. (activated alumina or silica gel )<\/p>\n
\n\udbc0\udc29 Incorrect condenser and evaporator temperature differential.
\n\udbc0\udc29 The system running longer than normal.
\n\udbc0\udc29 Difficult to cold down room temperature.<\/p>\n
\n\udbc0\udc23 Pumping down the entire charge to condenser.
\n\udbc0\udc23 Along the system must be blown out with compress air by stripping individual unit component.
\n\udbc0\udc23 Repair the oil separator.
\n\udbc0\udc23 Renew the compressor piston rings.<\/p>\n
\n1) Continuous running of compressor
\n2) Insufficient cooling effects
\n3) Noisy operation
\n4) High suction pressure<\/p>\n
\n1) Continuous running of compressor
\n2) Insufficient cooling effects
\n3) Noisy operation
\n4) High suction pressure during running
\n5) Low discharge pressure during running
\n6) Suction pressure faster after compressor is shut down
\n7) Warm cylinder head<\/p>\n
\n\udbc0\udc29 Occurs due to condenser coolant failure, low coolant pressure and malfunction of consider cooler valve operation.
\n\udbc0\udc29 Also can cause dirty or chocked condenser tubes.
\n\udbc0\udc29 The refrigerant can not liquefy rapidly .The discharge pressure will abnormally raise and high pressure cut out will take in action. Low pressure cut out
\n\udbc0\udc29 Operate the solenoid valve is closed when the cool room temp: reach its desired temp: (setting temp:)
\n\udbc0\udc29 Can cause when expansion valve is chocked by dirt or freeze up by water present in the system.
\n\udbc0\udc29 Starving of evaporator and rapid condenser pressure rise.
\n\udbc0\udc29 Compressor may stop by low pressure cut out.<\/p>\n
\nCO2 \u2013 Soap and water solution
\nNH3 \u2013Wet litmus paper (Red ~ Green); Sulphur candles, which gives off white dense smokes when contact with Ammonia
\nFreon \u2013 Soap and water solution \/ Halide torch \/Electronic leak detector (buzzer sound)
\nBy halide torch, How to indicate the flame ?
\nContent is methylated spirits type. Butane can also be used.
\nWhen the leak is detected the flame will change from blue to green depending on the concentration of gas.<\/p>\n
\nIt is a process in which the temperature of a space or its contents is reduced to below that of their surrounding.<\/p>\n
\nIt is the control of temperature and humidity in a space together with the circulation, filtering and refreshing of the air.<\/p>\n
\nIt is the circulation and refreshing of the air in the space without necessarily a change of temperature.<\/p>\n
\nIt is between the 40 to 70 % relative humidity at the temperature of 20 to 29C dry bulb temp:, air motion is 100mm per sec.<\/p>\n
\n\udbc0\udc09 Low initial cost
\n\udbc0\udc09 Low maintenance cost
\n\udbc0\udc09 Suitable for large refrigeration plant
\n\udbc0\udc09 Easily produce onboard by mixing Ca Cl2 and distilled water.
\n\udbc0\udc09 Easily store as a salt onboard
\nDefrosting<\/strong>
\nA method of removal of frost, built-up on Evaporator coils. Defrosting should be done before snow thickness exceeds \u00bc\u201d.<\/p>\n
\n\udbc0\udc29 Affecting heat transfer properties
\n\udbc0\udc29 Affecting air flow and circulation
\n\udbc0\udc29 Liquid back to compressor<\/p>\n
\n\udbc0\udc40 By stopping the system
\n\udbc0\udc40 By washing with warm water
\n\udbc0\udc40 By means of electric heater coil fitted at the evaporator
\n\udbc0\udc40 By hot gas defrosting method
\nDefrost brine System<\/strong>
\nHot brine thawing<\/strong> : Best and fastest method, used powerful brine heater with separate thawing system. Watertight trays under the pipes, collected the dripping water
\nHot air from atmosphere : It is important that isolating doors in air trunks are perfectly tight, so as to prevent hot air going into cargo spaces.
\nBy shutting off brine<\/strong> : Allow the snows to be melted by the heat of the heat of the air in circulation .Very slow operation and tends to throw back great deal of moisture into cargo space.<\/p>\n
\nBattery cooling system<\/strong> : Water spray, electrical or steam heater
\nBrine cooling<\/strong> : Hot brine thawing<\/p>\n
\n\udbc0\udc40 To remove surplus heat and humidity
\n\udbc0\udc40 To prevent the condensing of moisture on cargo or hull
\n\udbc0\udc40 To remove gases produced in ripening process of some fruits and vegetables cargos.<\/p>\n
\nIt is a condition of a compressor unit repeatedly running for a few second and then cutting out .This is the result of L.P controller.<\/p>\n
\nIt is fitted to shut down the compressor in the event of high pressure .After remedy the fault, have to run necessary to reset.<\/p>\n
\nIf compressor stops due to a fault, the master solenoid valve will close to prevent flooding by liquid refrigerant and possible compressor damage.<\/p>\n
\nNormally charging is made through the liquid charging valve at the high pressure side.
\n01). Firstly, weighting the gas bottle.
\n02). Connect the gas bottle and charging valve with the connection pipe.
\n03). Before tightening the cap on charging pipe, open bottle valve to remove air in the pipe.
\n04). Then tighten the cap and open bottle valve fully, charging valve is still closed.
\n05). Change compressor to manual running and start it.
\n06). Close the condenser outlet valve.
\n07). Pumping down the entire charge to the condenser.
\n08). Open the charging valve slowly when suction pressure just above zero.
\n09). Control the valve opening slowly that no frost formed on the compressor suction
\npipe.
\n10). Check the level in the condenser sight glass.
\n11). Close the charging valve and pumping down the entire charge until suction
\npressure just above zero.
\n12). Stop the compressor and close the discharge valve.
\n13). Cooling water kept running for some hour.
\n14). Then air is purged out through purging valve on condenser until the refrigerant
\ngas appear at the valve.
\n15). Calculate the amount of refrigerant (charging) and enter the engine log book.<\/p>\n
\n\udbc0\udc40 To prevent the liquid refrigerant entering into the compressor.
\n\udbc0\udc40 If no super heat, hammering may happen and the valve will suffer damage and breakage.<\/p>\n
\n01) Change the compressor to manual running.
\n02) Pumping down the entire charge to condenser.
\n03) Connect the L.O hand pump to L. O filling valve after air is purged out.
\n04) When compressor suction pressure just above zero, open the oil filling valve, inject the L.O into crank case.
\n05) Then stop the compressor and close compressor discharge valve. Then cool down the refrigerant.
\n06) Then purged out the air through the purging valve until refrigerant appears at purging valve.<\/p>\n
\n\udbc0\udc52 Thermostatic control
\n\udbc0\udc52 Electronic control
\n\udbc0\udc52 Manual control<\/p>\n
\n2) Liquid shock valve (on cylinder head0
\n3) TEV
\n4) Master solenoid valve (when the plant is standstill, especially in Large plant)
\n5) Defrosting
\n6) Bursting disc (on cylinder head, between inlet and discharge manifold)
\nBack pressure valve at the outlet of vegetable room to prevent under cooling of cargo.<\/p>\n