Refrigeration practitioner must master: Data Center Refrigeration System design 40 problems!
  1. What are the three necessary conditions for the safe operation of refrigeration system?


(1) The refrigerant pressure in the system shall not be abnormally high pressure, so as to avoid the rupture of the equipment.

(2) Shall not occur (may lead to) wet stroke, liquid explosion, liquid strike and other misoperation, so as to avoid equipment damage.

(3) The moving parts shall not have defects or loose fasteners, so as not to damage the machinery.


2.What is the evaporation temperature?


(1) The temperature of the refrigerant in the evaporator when it boils and vaporizes under a certain pressure is called the evaporation temperature.


3.What is the condensation temperature?


(1) The temperature at which the gas refrigerant in the condenser condenses into a liquid under a certain pressure is called the condensation temperature.


4.What is the recooling (or supercooling) temperature?

A: (1) The temperature at which the condensed liquid refrigerant is cooled below the condensing temperature under the condensing pressure is called the recooling temperature (or supercooling temperature).


5.What is the intermediate temperature?

A: (1) Two-stage compression system, the saturation temperature of the refrigerant in the intercooler under the intermediate pressure is called the intermediate temperature.


6. (how to detect, how to control) compressor suction temperature?

A: (1) The suction temperature of the compressor can be measured from the thermometer in front of the suction valve of the compressor. The suction temperature is generally higher than the evaporation temperature, and the higher difference depends on the length of the return pipe and the pipe insulation condition. Generally, it should be 5~10 higher than the evaporation temperature. Changing the liquid supply can adjust the superheat.


7. (how to detect) compressor exhaust temperature, (exhaust temperature affected by what factors)?

A: (1) The exhaust temperature of the compressor can be measured from the thermometer on the exhaust pipe. The exhaust temperature is proportional to the pressure ratio and the suction temperature. The higher the suction superheat and pressure ratio, the higher the exhaust temperature; Otherwise, the opposite. Generally, the exhaust pressure is slightly higher than the condensation pressure.


  1. What is a Wet car (liquid attack)?

A: (1) Refrigerant liquid or wet steam is sucked into the compressor by the compressor due to failure or insufficient endothermic evaporation of refrigerant.


8.What causes Wet car?

A: (1) The liquid level control of the gas-liquid separator or the low pressure circulation barrel fails, resulting in the ultra-high liquid level.

(2) the liquid supply is too large, the liquid supply is too urgent. The throttle valve leaks or opens too large.

(3) The evaporator or gas-liquid separator (low pressure circulation barrel) holds too much liquid, the heat load is small, and the load is too fast when starting up.

(4) Sudden increase of heat load; Or did not adjust the suction valve after the frost.


9.What will happen after the Wet car?

A: For the piston machine: (1) the refrigerant enters the compressor, which makes the lubricating oil produce a large number of bubbles, destroy the oil film on the lubricating surface, and make the oil pressure unstable.

(2) Make the moving parts run under the condition of no good lubrication, leading to hair drawing; In serious cases, the holding shaft, the main shaft wabbitt alloy melting.

(3) The refrigerant enters the compressor, causing the cylinder liner to shrink sharply and hug the piston; Damage cylinder liner, piston, connecting rod and piston pin in severe cases.

(4) Because the liquid is incompressible, the connecting rod and piston are subjected to far more force than the design value, which is easy to cause damage; Because the liquid is incompressible, the exhaust valve set together with the false cover will be lifted by the impact of the liquid in the case of the tide truck; Serious will lead to the deformation of the safety spring, and even crash into the body, cylinder head, breakdown gasket and personal injury.

For screw machine: damp car will cause vibration, increase noise, rotor and bearing (too much stress) damage; Severe hipsters can also damage equipment and cause accidents.


10.How to deal with the Wet car?

A: (1) When the piston compressor is damp, the suction stop valve of the compressor should be turned down immediately, and the throttle valve should be closed to stop the liquid supply. If the suction temperature continues to decrease, continue to turn down or even close the suction valve, and unload it until it is reduced to zero. Use the friction heat between the crankshaft and the bearing bush to vaporize the refrigerant in the crankcase. When the pressure in the crankcase rises, put a group of cylinders to work, and then unload after the pressure decreases. Repeat several times until the refrigerant in the crankcase completely evaporates. After that, slightly open the suction stop valve and slowly increase the load. If there is still refrigerant liquid in the suction line, repeat the previous process. Until the liquid is completely drained, slowly open the suction stop valve, the compressor into normal work. When the tide car occurs, attention should be paid to observe and adjust the oil pressure. If there is no oil pressure or the oil pressure is too low, the machine should be shut down immediately, and the lubricating oil and refrigerant in the crankcase should be released. When the damp car occurs in the screw compressor, the suction stop valve of the compressor should be turned off immediately, and the throttle valve should be closed to stop the liquid supply. If the suction temperature continues to decrease, continue to turn down but not close the suction valve to prevent abnormal sound and vibration caused by too low suction pressure, and reduce the load until it is reduced to zero. The screw compressor is not sensitive to wet stroke, and the liquid in the return pipe is slowly discharged into the oil fraction. Then open the suction stop valve and slowly increase the load until the compressor is put into normal operation. When tide car occurs, attention should be paid to observe and adjust the oil pressure. To prevent the oil temperature from being too low, turn on the oil heating equipment or turn down the oil cooling water valve.


11.What causes the exhaust pressure is too high, how to exclude?

A: (1) The system and high pressure part of the mixed gas will cause high exhaust pressure. Air should be released. In ammonia system, in order to reduce ammonia pollution to the atmosphere, air separator is generally used to discharge non-condensable gas in the system.

Small fluorine system can be directly discharged through the air vent valve on the condenser. Open the air valve slightly for air release. When the discharged gas is white smoke, indicating that more freon is released, the valve should be closed to end the air release operation.

(2) There is scaling or accumulation of debris on the water side of the condenser heat exchange tube. The water cover on both sides of the condenser should be opened for inspection and cleaning (rinse with a high-pressure water gun, wipe with a brush or cloth strip, please be cleaned by a professional company).

(3) Excessive liquid accumulation and oil accumulation in the condenser. Check whether the outlet valve and the balance pipe valve of the condenser are fully opened (they should be fully opened), and check whether the valve head falls off if necessary. Release excessive refrigerant and accumulated refrigerant oil.

(4) The separation gasket of condenser end cover is damaged, resulting in short circuit circulation of cooling water. The water cover on both sides of the condenser should be opened, the rust of the parting pad should be removed, and the rubber pad should be replaced.

(5) The inlet and outlet temperature of cooling water exceeds the design requirements. Clean the sewage of the cooling water tower, check whether the water distributor falls off and tilts, and whether the water inlet is blocked by foreign matter.

(6) insufficient cooling water flow. The temperature difference of cooling water in and out exceeds the requirements. Check: whether the pump mechanical wear is too large; Whether there is foreign body blockage in the pump; Water valve, check valve, filter screen is abnormal; Whether the head of the pump meets the requirements; Whether the water pipe route and specifications are reasonable.


13. The compressor can not start up the cause and treatment method?

A: (1) Electrical failure; Check and repair.

(2) failure of pressure relay or oil pressure relay; Check and adjust interlocking contacts of pressure relay and oil pressure relay.

(3) the crankcase pressure or intermediate pressure is too high; Repair the exhaust valve disc or reduce the crankcase and intermediate pressure.

(4) (piston machine) unloading mechanism failure; Check and repair.

14.The piston machine cylinder inside the knock sound reason and treatment method?

A: (1) When running, the piston hits the exhaust valve; Open the noisy cylinder head to increase the clearance between the piston and the inner seat

(2) The air valve bolt is loose; Tighten the valve bolts.

(3) The valve disc is broken and falls into the cylinder, and the clearance between the small head of the piston pin and the connecting rod is too large, and the clearance between the piston and the cylinder is too large; Check, adjust and repair after cylinder removal.

(4) The false cover spring is deformed and the elastic force is not enough; Pad to increase spring force or replace.

(5) Refrigerant liquid enters the cylinder and causes liquid percussion; Turn the suction stop valve down, the liquid supply throttle valve down or temporarily close to remove the liquid.


15. The piston crankcase inside the knock sound reason and treatment method?

A: (1) the gap between the connecting rod big head bearing bush and the crank pin is too large; Check and adjust its clearance or replace it.

(2) The clearance between the spindle neck and the main bearing is too large; Check the adjustment clearance.

(3) the flywheel is relaxed with the shaft or key; Check and adjust the clearance and repair.

(4) The cotter pin of the connecting rod bolt is broken and the connecting rod nut is loose; Tighten connecting rod nut and lock with cotter pin.


16.Piston compressor after the start of no oil pressure causes and treatment methods?

A: (1) The transmission parts of the oil pump fail; Disassemble and repair.

(2) The oil inlet of the oil pump is blocked; Check to remove dirt.

(3) Oil pressure gauge failure; Replace the oil pressure gauge.

(4) Oil filter and shaft seal without oil; Before driving, oil should be added to the fine oil filter and shaft seal to prevent empty suction during driving.


17.Piston compressor oil pressure is too low cause and treatment method?

A: (1) The oil filter is blocked; Remove and clean.

(2) Oil pressure regulating valve failure; Repair or replace.

(3) The clearance between the oil pump gear and the pump cover is too large and worn; Repair or replace.

(4) Crankcase oil level is too low; Add oil or return oil from oil.

(5) Serious wear of bearings in all parts causes excessive clearance or oil leakage in some oil routes; Check and repair.


18.Piston compressor fuel consumption increases the cause and treatment method?

A: (1) Refrigerant liquid enters the crankcase; Turn down or temporarily close the suction stop valve and the supply throttle valve (refer to the method for dealing with the tide truck).

(2) The sealing ring, oil scraping ring or cylinder is seriously worn or the piston ring lock is in a line; Check, adjust, and replace badly worn parts if necessary.

(3) The crankcase oil level is too high or the exhaust temperature is too high; Release some lubricating oil or take measures to reduce the exhaust temperature.


19.What is the cause of oil leakage or air leakage of shaft seal and how to deal with it?

A: (1) Shaft seal assembly is bad or shaft seal sealing surface hair pulled; Check and adjust, replace or grind the seal ring.

(2) The "O" ring of the dynamic and static rings is aging and deformed or the tightness is not appropriate; Replace the sealing rubber ring.

(3) The liquid refrigerant content in the oil is much; Increase oil temperature or discharge refrigerant.

(4) The crankcase pressure of piston compressor is too high; Reduce crankcase pressure.


20.Piston compressor unloading device mechanism failure causes and treatment methods?

A: (1) Insufficient oil pressure; Adjust the oil pressure so that the oil pressure is 0.12 to 0.2MPa higher than the suction pressure.

(2) The tubing is blocked; Disassemble and clean.

(3) There is dirt stuck in the oil cylinder; Disassemble and clean.

(4) Improper assembly of oil distribution valve, incorrect assembly of tie rod or rotating ring, rotating ring stuck; Disassemble and repair.


21.The compressor suction superheat (suction temperature is higher than the evaporation temperature) is too large cause and treatment method?

A: (1) Insufficient refrigerant in the refrigeration system; Add refrigerant.

(2) Insufficient refrigerant in the evaporator; Open the throttle valve and increase the liquid supply.

(3) The suction pipe of the refrigeration system is not well insulated; Check and repair.

(4) Excessive water content in refrigerant; Check the water content of the refrigerant.

(5) Throttle valve opening is small, small liquid supply; Open the throttle valve and increase the liquid supply.


22.Piston compressor exhaust temperature is high cause and treatment method?

A: (1) The suction gas temperature is too high; Adjust suction superheat (refer to question 21).

(2) The exhaust valve disc is broken; Open the cylinder head, check and replace the exhaust valve disc.

(3) Safety valve leakage; Check the safety valve, adjust and repair.

(4) Piston ring leakage; Check piston ring, adjust repair.

(5) The cylinder liner gasket is broken and leaking; Check the replacement.

(6) The dead point clearance of the piston is too large; Check and adjust the top dead space.

(7) Insufficient cooling capacity of cylinder cover; Check the amount of water and water temperature, adjust.

(8) The compressor compression ratio is too large; Check evaporation pressure and condensation pressure.


23.Compressor suction pressure is too low cause and treatment method?

A: (1) The liquid supply throttle or suction filter is blocked (dirty or ice blocked); Disassemble, check and clean.

(2) Insufficient refrigerant in the system; Add refrigerant.

(3) Insufficient refrigerant in the evaporator; Open the throttle valve and increase the liquid supply.

(4) Too much frozen oil in the system and evaporator; Find out where the oil accumulates in the system and discharge the oil.

(5) Small heat load; Adjust the compressor energy level and unload properly.


24.Screw unit abnormal vibration causes and treatment methods?

(1) The foundation bolt of the unit is not tightened or loosened; Tighten the anchor bolts.

(2) The compressor shaft and the motor shaft are misaligned or have different centers; Get it right again.

(3) Pipeline vibration causes the unit vibration intensification; Add or change the point of support.

(4) The compressor inhales too much oil or refrigerant liquid; Shut down and turn over to drain the liquid from the compressor.

(5) The spool valve can not stop at the required position, but vibrate there; Check oil piston, four-way valve or load - increasing solenoid valve for leakage and repair.

(6) The vacuum degree of suction chamber is too high; Open the suction stop valve and check whether the suction filter is blocked.


25.Screw unit refrigeration capacity is insufficient cause and treatment method?

A: (1) The position of the spool valve is not appropriate or other failures (the spool valve cannot rely on the fixed end); Check the position of indicator or angular displacement sensor and repair spool valve.

(2) The suction filter is blocked, the suction pressure loss is too large, the suction pressure drops, the volume efficiency decreases; Remove air filter and clean.

(3) Abnormal wear of the machine, resulting in excessive clearance; Check, adjust or replace parts.

(4) The suction line resistance loss is too large, the suction pressure is too low than the evaporation pressure; Check the suction stop valve and suction check valve, find problems and repair.

(5) Leakage between high and low pressure systems; Check the driving and parking bypass valves and oil return valves to repair any problems found.

(6) Insufficient oil injection, can not achieve sealing effect; Check the oil circuit, oil pump, oil filter, improve the oil injection.

(7) The exhaust pressure is much higher than the condensing pressure, and the volumetric efficiency decreases; Check the exhaust piping and valves to clear the resistance of the exhaust system. If the system seeps into the air should be discharged.


26.Screw unit in the operation of abnormal sound causes and treatment methods?

A: (1) There are sundries in the rotor groove; Check the rotor and suction filter.

(2) Thrust bearing damage; Replace thrust bearings.

(3) Main bearing wear, rotor and body friction; Overhaul and replace the main bearing.

(4) Slide valve deflection; Repair the spool valve guide block and guide column.

(5) The connection of moving parts is loose; Disassemble the machine for maintenance and strengthen relaxation measures.


27.Causes and treatment of excessive exhaust temperature or oil temperature?

A: (1) The compression ratio is too large; Detect suction and exhaust pressure to reduce pressure ratio.

(2) The cooling effect of water-cooled oil cooler decreases; Clean the oil cooler to lower the water temperature or increase the water volume.

(3) The liquid supply of liquid ammonia oil cooler is insufficient; Analyze the reason and increase the liquid supply.

(4) Inhalation of seriously overheated steam; Increase the liquid supply, strengthen the insulation of the suction line, and check whether the bypass valve leaks.

(5) Insufficient fuel injection; Check, analyze the cause, increase the injection amount.

(6) Air infiltration into the system; Should be discharged, and check the cause of air infiltration, maintenance.


28.(screw machine) Exhaust temperature or oil temperature drop causes and treatment methods?

A: (1) Inhalation of wet vapor or liquid refrigerant; Reduce the amount of liquid supplied to the evaporation system.

(2) Continuous no-load operation; Check the spool valve.

(3) The exhaust pressure is abnormally low; Reduce the water supply or the number of condenser input.


29.(screw machine) Spool valve action is not flexible or do not act the reason and treatment method?

A: (1) Four-way reversing valve or solenoid valve action is not flexible; Check the coils and wiring of the four-way reversing valve or solenoid valve.

(2) The oil pipeline system is blocked; Overhaul.

(3) Oil piston stuck or leaking oil; Repair the oil piston or replace the sealing ring.

(4) Oil pressure is too low; Check and adjust oil pressure.

(5) The spool valve or guide key is stuck; Overhaul.


30.Screw compressor body temperature is too high cause and treatment method?

A: (1) Abnormal wear and tear of moving parts; Repair compressor and replace damaged parts.

(2) Severe overheating on inhalation; Reduce suction superheat.

(3) Bypass pipeline leakage; Check the starting and parking bypass valves for leaks.

(4) The compression ratio is too large; Detect suction and exhaust pressure to reduce pressure ratio.


31.Causes and treatment of compressor and oil pump shaft seal leakage?

A: (1) The shaft seal is damaged due to insufficient oil supply; Repair, check oil circuit, adjust oil pressure.

(2) "O" ring deformation or damage; Replace it.

(3) Poor assembly; Demolition, inspection and repair.

(4) The contact between static and static rings is not tight; Remove and re-grind.

(5) Impurities in the oil wear the sealing surface, too much refrigerant liquid in the oil; Check essential oil filter to ensure oil supply temperature.


32.The cause and treatment of low oil pressure?

A: (1) Improper adjustment of oil pressure regulating valve; Adjust the oil pressure regulating valve again.

(2) The internal oil leakage of the compressor is large; Check and repair.

(3) The oil temperature is too high; Check the oil cooler to exclude factors affecting the heat transfer capacity.

(4) Inferior oil quality and insufficient oil quantity; Change and add oil.

(5) Oil pump wear or failure; Overhaul.

(6) Crude oil, fine filter dirty blocking; Clean the filter element.

(7) Oil contains more refrigerant; Shut down and heat oil.


33.Compressor fuel consumption increases the cause and treatment method?

A: (1) The oil separation efficiency of the oil separator decreases; Check the oil separator.

(2) There is too much oil in the oil separator, and the oil level is too high; Drain oil and control oil level.

(3) The exhaust temperature is too high, and the efficiency of the oil separator decreases; Strengthen oil cooling and reduce exhaust temperature.

(4) The oil pressure is too high, the oil injection is too much, the compressor liquid return; Adjust the oil pressure or repair the compressor and deal with the liquid return of the compressor.

(5) The return pipeline is blocked; Overhaul.


34.Oil separator oil surface rise cause and treatment method?

A: (1) The oil in the system returns to the compressor; Too much oil is released.

(2) Too much refrigerant enters the refrigerant oil; Increase the temperature of the oil and accelerate the evaporation of the refrigerant dissolved in the oil.

(3) The oil separator return pipeline is blocked; Overhaul.

(4) The liquid level meter of vertical oil separator has condensed refrigerant liquid; At this time the liquid level height may not be true, should estimate the actual oil level height.


35.The cause and treatment of compressor inversion when screw compressor stops?

A: (1) The suction and exhaust check valves are not tightly closed; Repair and eliminate the valve plate stuck.

(2) To prevent the reverse bypass pipeline valve is not opened in time; Check and repair.


36.Why is the suction temperature too low and how to deal with it?

A: (1) Too much refrigerant in the evaporator, gas-liquid separator or low pressure circulation barrel; Adjust the liquid supply valve, stop or reduce the amount of liquid supply, and even discharge excessive refrigerant to the liquid discharge bucket.

(3) The evaporator heat transfer efficiency is reduced; Clean the evaporator or drain the oil.


37.How is the safety protection value of refrigeration equipment and the vacuum test of the system stipulated?

A: Refrigeration equipment safety protection value according to the product instruction manual. The safety protection values of LG series screw refrigeration compressor are as follows (for reference) :

(1) Injection temperature high protection: 65(shut down);

(2) Low suction pressure protection: -0.03Mpa (shutdown), this value can be modified;

(3) High exhaust pressure protection: 1.57Mpa (shutdown);

(4) Oil filter pressure differential high protection: 0.1Mpa (shut down);

(5) Overload protection of the main motor (protection value according to the requirements of the motor);

(6) Low protection between oil pressure and exhaust pressure: 0.1Mpa (shutdown);

(7) Overload protection of oil pump (protection value according to the requirements of the motor);

(8) Low outlet temperature protection for water chiller, brine unit and ethylene glycol unit, and water cut-off protection for evaporator and condenser.

(9) Condenser, liquid reservoir, oil separator, oil collector safety valve opening pressure: 1.85Mpa; Full liquid evaporator, gas-liquid separator, low pressure circulation liquid storage barrel, intercooler, economy valve opening pressure: 1.25Mpa.


Vacuum test of the system:

The purpose of vacuum test of the system is to check the tightness of the system under vacuum and prepare for the filling of refrigerant and refrigerant oil. Pump the system to 5.33kpa (40mm Hg) and hold for 24h. The pressure rise should not exceed 0.67kpa (5mm Hg).


38.How to arrange major, medium and minor equipment repair?

A: (1) The cycle of major, medium and minor repair of the equipment shall be arranged by the user according to the provisions of the equipment operation manual and considering the user's operating environment, operating conditions, annual driving time, production beat and other characteristics. Timely maintenance. The contents of major, medium and minor repairs of the equipment shall be determined according to the instructions of the equipment and the specific use of the equipment.


39.How to arrange the large, medium and small repair of piston refrigeration compressor? (for reference)

(1) What is the period of overhaul?

A: (1) Overhaul every 8,000 hours or so.

(2) What is the content of the overhaul?

A: (2) Check and clean the parts, and measure the wear degree of the parts: such as cylinder, piston, piston ring, crankshaft, bearing, connecting rod, suction and exhaust valve, oil pump, etc. Wear slight can be trimmed use, wear heavy should be replaced. Inspection of safety valves and instruments (should be carried out by qualified departments). Clean the filter of refrigerant oil system, refrigerant system and water system.

(3) What is the period of intermediate repair?

A: (3) Intermediate repair every 3000-4000 hours or so.

(4) What is the content of the middle course?

A: (4) Except for minor repairs, check and calibrate the clearance between cylinder and piston, the clearance between piston ring lock, the clearance between connecting rod size head and crank pin, the clearance between main bearing and main axle diameter, the clearance between air valve and piston, etc. Check piston pin, cylinder, crankshaft and other parts wear degree. Check the lubrication system. Check whether the coupling and anchor bolts are loose.

(5) What is the period of minor repair?

Answer: (5) After the medium repair, a minor repair is carried out every 1000-1200 hours or so.

(6) What is the content of minor repair?

A: (6) Clean the cooling water pump; Check piston, gas ring, oil ring and suction and exhaust valve, replace the damaged valve disc and valve spring, etc. Check the size of connecting rod head bearing, cleaning crankcase, oil filter and suction filter, etc.; Change the freezer oil; Check the coaxiality of the motor and the crankshaft.


40.How to arrange the large, medium and small repair of screw refrigeration compressor? (for reference)

The maintenance period of screw compressor unit is related to many factors. The following information is for reference.

A: (1) The motor of screw compressor: disassembly, maintenance and replacement, bearing refueling, period of 2 years, see the motor instruction manual.

(2) coupling: check the coaxiality of the compressor and the motor (check whether the elastic transmission piece is damaged or the rubber pin is worn). The term is 3-6 months.

(3) Oil separator: clean the interior, the term is 2 years.

(4) Oil cooler: remove scale (water cooling), oil scale, period of half a year; Subject to water quality and dirt condition.

(5) Oil pump: leak test and maintenance, period of 1 year.

(6) Oil filter (including crude oil filter), suction filter: cleaning, period of half a year. The first driving 100-150 hours should be cleaned.

(7) oil pressure regulating valve: regulating capacity inspection, period of 1 year.

(8) Spool valve: action inspection, period of 3-6 months.

(9) Safety valve, pressure gauge, thermometer: check, the term of 1 year.

(10) Check valve, suction and exhaust cut-off valve, pressure gauge valve: maintenance, period of 2 years.

(11) Pressure relay, temperature relay: check, the term is about half a year. Refer to the instructions.

(12) Electrical equipment: action inspection, the period of about 3 months. Refer to the instructions.

(13) Automatic protection and automatic control system: the term is about 3 months.

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Post time: Nov-29-2022
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