What are the guidelines for maintaining piston-type combined compressors?

It’s from the maintenance procedures; it’s quite simple. Cause, Phenomenon, and Solution Methods
Over-temperature/over-pressure: a) Damage to the check valve seat or disc; b) Blockage in the cooling water jacket. 1. Stop the machine and replace the seat and disc; 2. Clean the cooling water jacket.

Drop in oil pressure: (1) Failure of the oil pump control valve; (2) Blockage in the oil pump filter; (3) Blockage or air leakage in the suction oil pipe. 1. Re-calibrate the control valve; 2. Clean the filter; 3. Disassemble the oil pipe for cleaning and to fix leaks.

Increased bearing temperature: (1) Insufficient supply of lubricating oil; (2) Poor quality of lubricating oil; (3) Excessively small bearing clearance. 1. Inspect and clean the oil circuit; 2. Replace the lubricating oil; 3. Increase the bearing clearance.

Heating in the packing box: Too small axial clearance in the packing – increase the clearance. Air leakage in the packing box: (1) Severe wear of the packing; (2) Dirty gas. 1. Replace the packing; 2. Purify the gas.

Abnormal noises: 1. Loose bolts on the suction and discharge valve caps; 2. Debris entering the cylinder; 3. Excessively small cylinder clearance; 4. Loose connecting rod bolts; 5. Excessively large bearing clearance; 6. Vibration in the pipes. 1. Tighten the bolts; 2. Stop the machine and inspect the cylinder to remove debris; 3. Adjust the cylinder clearance; 4. Tighten the connecting rod bolts; 5. Adjust the bearing clearance; 6. Strengthen the pipes to eliminate vibration

Maintenance methods and quality standards 4.1 Maintenance methods 4.1.1 Use a level to measure the levelness of the fuselage； Measure the coaxiality of the middle body and the cylinder using the tensioning method and make adjustments accordingly. 4.1.2 Use the coloring method to check the contact area of the sliding bearing; if it does not meet the standard requirements, scraping and lapping should be carried out. 4.1.3 Use calipers, inside and outside diameter micrometers, and dial indicators to measure cylindricity and roundness; if the standards are not met, grinding should be performed, and if necessary, measurements or machining should be carried out using machine tools. 4.1.4 Use a feeler gauge to measure the radial clearances between the piston and the cylinder, as well as between the packing and the piston rod, and make adjustments accordingly. 4.1.5 Measure bearing clearance, gear mesh clearance, and cylinder clearance using the lead pressure method. 4.1.6 Use colored and non-destructive testing methods to inspect defects such as cracks in parts. 4.1.7 The main and crankshaft journals, as well as the piston rods, can be repaired using methods such as electroplating, spray plating, and brush plating. 4.2 Maintenance Quality Standards 4.2.1 Foundation 4.2.1.1 Visual inspection shall not reveal any defects such as cracks, looseness, exposed rebar, oil seepage, or concrete spalling. 4.2.1.2 The foundation shows no uneven settlement or inclination. 4.2.2 Frame and Middle Body 4.2.2.1 The longitudinal and transverse irregularities of the frame are 0.05 mm/m. 4.2.2.2 The perpendicularity between the center line of the crosshead slide and the center line of the main shaft hole is 0.01 mm/m. 4.2.2.3 The coaxiality between the center line of the main bearing of the frame and the center line of the auxiliary bearing hole of the motor is 0.03 mm. 4.2.2.4 The cylindricity of the frame slides is 0.5 mm. 4.2.2.5 The allowable deviations for the coaxiality between the cylinder center line and the slide are shown in the table below: Cylinder Diameter Parallel Displacement Axial Tilt <100 >100–300 >300–500 0.05 0.07 0.10 0.02/1000 0.02/1000 0.04/1000 1. The parallelism between the center lines of the various slides after assembly is 0.1 mm/m. 2. A leak test must be conducted on the oil tank of the frame, with no leaks allowed within 4 hours. 4.2.3 Crankshaft and bearings 4.2.3.1 The crankshaft shall be inspected under a magnifying glass or through non-destructive testing; it must be free of cracks. The area of wear on the main bearings and crankshaft journals shall not exceed 2%, and the depth of wear shall not be greater than 0.01 mm ； Mechanical processing is required when the limit is exceeded, and the reduction in size resulting from such processing shall not exceed 1% of the original journal diameter. 4.2.3.2 The levelness of the crankshaft installation is 0.10 mm/m. 4.2.3.3 The variation in the crankshaft’s opening angle is ≤10-4 s; after the motor is installed, this value is ≤3×10-4 s (where s is the stroke, in mm). 4.2.3.4 The radial runout of the main journal is 0.05 mm ； The coaxiality of each main journal is 0.03 mm. 4.2.3.5 The requirements for the roundness and cylindricity of journals after repair are shown in the table below: mm Journal diameter <100 >100–200 >200–300 >300–400 >400–500 Roundness Cylindricity Main journal 0.06 0.08 0.10 0.12 0.14 Crank journal 0.08 0.10 0.12 0.14 0.16 1. Sliding bearings a. The contact area between the bearing shell and the bearing hole shall be at least 60%, and the contact area between the main journal and the main bearing shall be at least 70% ； b. The fit between the main journal and the main bearing is generally H7/d8; the radial clearance is (0.8–1.2)×10-3d (where d is the diameter of the main journal, in mm), while the axial clearance is 0.2–0.5 mm. c. When the thickness wear of a thick-walled bearing exceeds 60% of its original thickness, or when the area of chipping or flaking reaches 15%, it should be remolded. 2. Rolling bearings a. Rolling bearings should rotate smoothly without any noise, and the rolling surfaces of the rollers as well as the inner and outer rings should be free from defects such as rust or pitting ； b. The fit between the inner ring of the rolling bearing and the shaft is H7/k6, while the fit between the outer ring and the inner hole of the bearing housing is J7/h6. 4.2.4 Connecting rods and crossheads 4.2.4.1 The straightness of the connecting rod is 1 mm/m. 4.2.4.2 The parallelism between the centerlines of the large and small ends of the connecting rod is 0.05 mm/m, and the cylindricity of the holes shall not exceed 1 time the tolerance on the diameter dimension. 4.2.4.3 The crosshead and crosshead pin shall be free from defects such as cracks when inspected under a magnifying glass or through non-destructive testing. 4.2.4.4 Radial clearance of crosshead bearings and crosshead pins: a. For copper alloy bearings, it is (0.7—1.2)×10-3d (where d is the diameter of the crosshead pin, in mm) ； b. The babbitt bearing value is (0.4~0.6)×10-3d (where d is the diameter of the crosshead pin, in mm) ； 4.2.4.5 Interference fit amount between the integral connecting rod cap bearing and the connecting rod hole: 0.02~0.08 mm for copper alloy bearings ； The steel-cased babbitt bearing thickness is 0.05~0.10 mm. 4.2.4.6 The contact area between the big end bearing of the connecting rod and the crank journal must be at least 70%, with a radial clearance of 0.0006~0.0008D (where D is the diameter of the crank journal, in mm). 4.2.4.7 The axial clearance of the connecting rod is generally 0.30~1 mm ； The non-positioning axial clearance is 2~5mm. 4.2.4.8 The crosshead bearing and slideway should be in even contact, with a radial clearance of (0.6~0.8)×10-3d (where d is the outer diameter of the crosshead). 4.2.4.9 The perpendicularity between the end face of the crosshead neck and the slide track shall be 0.2 mm/m. 4.2.4.10 The requirements for the roundness and cylindricity of the crosshead pin are shown in the table below: Crosshead pin diameter <40, 40–70, >70; Roundness, Cylindricity: 0.01, 0.015, 0.02 respectively. 4.2.4.11 The connecting rod bolts must not have any cracks when inspected under a magnifying glass or through non-destructive testing methods ； When the bolts are tightened, their elongation shall not exceed 0.1% of their original length. 4.2.5 Piston and piston rings 4.2.5.1 Pistons and piston rings must be inspected under a magnifying glass or through non-destructive testing to ensure that there are no cracks, pores, scars, or other defects. 4.2.5.2 The wear-resistant support surface at the lower part of the piston should make even contact; the wear on this support surface shall not exceed 1/2 of its original thickness, and cracking or flaking is not allowed. 4.2.5.3 Radial clearance after installation of the piston and cylinder: For horizontal cylinders, when there is a wear-resistant support at the lower part of the piston, the upper clearance is (0.0008~0.002)D (where D is the diameter of the cylinder, in mm). 4.2.5.4 After piston wear, its roundness and cylindricity shall meet the requirements specified in the table below. Cylinder inner diameter: 100–150, >150–400, >400–550, >550–700, >700–850, >850–1000. Roundness: 0.20, 0.30, 0.45, 0.55, 0.60, 0.65. Cylindricity: 0.15, 0.25, 0.45, 0.55, 0.65, 0.70. The coaxiality between the piston’s centerline and the piston rod’s centerline is 0.05 mm. 4.2.5.6 The perpendicularity between the centerline of the piston rod hole and the supporting surface of the piston shoulder is 0.2 mm/m ； The perpendicularity between the two end surfaces of the piston ring groove and the centerline of the piston rod hole is 0.2 mm/m. 4.2.5.7 The sharp corners on the outer circumference of the piston ring should be rounded into small fillets, while the sharp corners on the inner circumference should be at 45 degrees. Angles; dimensions are shown in the table below. Piston outer diameter: D ≤250, >250~500, >500. Chamfer angle C×45: ≤0.50, ≤1.00, ≤1.50. Radius of rounding: ≤0.25, ≤0.40, ≤0.80. 4.2.5.8 The radial wear of the piston rings shall not exceed 20% of their original thickness, and the flatness of the two axial surfaces shall be 0.05 mm. 4.2.5.9 When the piston ring is placed in the special gauge, its outer surface should fit tightly; when inspected with a light, there should be no more than 2 gaps along the entire circumference, and the length of each gap shall not exceed 45. The arc length corresponding to the central angle ； At least 30 from the opening. The length of the arc corresponding to the central angle. 4.2.5.10 The piston rings are placed in the piston ring grooves; under conditions that restrict free expansion, they sink by 0.3~0.5 mm ； The fit between the inner circle of the piston ring and the outer circle of the bottom of the piston ring groove is H8/d8; the values for the radial clearance are shown in the table below: Piston ring outer diameter <250, 250–500, >500 – Radial clearance ≤0.03, ≤0.05, ≤0.08. 4.2.5.11 Opening clearance and axial clearance after the piston ring is installed in the cylinder: a. The opening clearance and axial clearance for cast-iron piston rings are given in the table below. Piston ring outer diameter: 100–200, >200–300, >300–400, >400–500, >500–700 – Opening clearance: 0.4–0.9, >0.9–1.4, >1.4–1.6, >1.6–1.8, >1.8–2.3 – Axial clearance: 0.03–0.06, >0.06–0.08, >0.08–0.12, >0.12–0.14, >0.14–0.16. 4.2.5.12 The allowable clearance when the piston ring is installed in the cylinder, under the conditions specified in clause 4.2.5.9 of these regulations, is shown in the table below: Piston ring outer diameter – Allowable clearance: ≤250, 0.03; >500–800, 0.08; >250–500, 0.05; >800, 0.12. 4.2.6 Piston rod: 1. The piston rod must not have any cracks, as determined through inspection using a magnifying glass or other testing methods. 2. The straightness of the piston rod is 0.05 mm/m. 3. After installation, the swing amount of the piston rod shall not exceed 0.10 mm/m. 4. The requirements for the roundness and cylindricity of piston rods are specified in the table below: 4.2.7 Cylinders, cylinder liners – Piston rod diameter: Required after repair; Maximum allowable wear value; Roundness, cylindricity. Roundness, cylindricity; Diameter reduction: 35–50, >50–80, 80–120. Values: 0.01 for b), 0.015 for a), 0.02 for a), 0.03 for a), 0.05 for a), 0.07 for a), 0.10 for a), 0.15 for a); 0.20. 4.2.7.1 The inner wall of the cylinder should be smooth, free from defects such as cracks, sand holes, rust spots, and roughness ； If the roughened groove exceeds 1/4 of the circumference or the groove depth exceeds 0.5 mm, the cylinder should be bored or a liner installed; the increase in the cylinder bore diameter shall not exceed 2% of the original cylinder diameter, and the decrease in wall thickness shall not exceed 1/12 of the original wall thickness. After the cylinder diameter is increased, the increase in piston thrust does not exceed 10% of the design value. 4.2.7.2 The roundness, cylindricity, and uniform wear values of the cylinders are shown in the table below: Cylinder inner diameter, Roundness, Cylindricity, Uniform wear: 100–150: 0.15, 0.05, 0.30; >150–300: 0.20, 0.10, 0.60; >300–450: 0.25, 0.15, 0.80; >450–600: 0.30, 0.20, 0.10; >600–800: 0.35, 0.25, 0.12. 1. The interference fit between the cylinder and the cylinder liner is: (0.00005–0.0002)d (where d is the outer diameter of the cylinder liner, in mm). 2. The horizontality of cylinder installation is 0.05 mm/m. 3. Cylinder hydrostatic test: i. When the design pressure is < 10 MPa, the test pressure shall be 1.5 times the design pressure, but shall not be less than 0.5 MPa ； ii. When the design pressure is ≥ 10 MPa, the test pressure is 1.25 times the design pressure ； iii. The test pressure for the cylinder cooling water jacket is 0.5 MPa. 4.2.7.6 The clearance between the cylinder and the piston shall comply with the specifications in the following table: Cylinder diameter – Front clearance – Rear clearance: 100~150: 3.0~4.6; 20; >150~200: 3.0~4.6; 2.0~2.9; >200~300: 2.3~3.7; 2.0~2.4; >300~400: 2.3~3.7; 2.0~2.4; >400~700: 2.3~3.7; 2.0~2.4. 4. After the cylinder connection bolts are tightened, the perpendicularity of the connection surface should be 1 mm/m, and after tightening, the nut should make even contact with the connection support surface. 4.2.8 Valve disc and valve seat 1. The surfaces of the valve disc, valve seat, and lift limiter should be flat and smooth; no defects such as cracks, scratches, pitting, or rust spots are allowed. The valve disc fits tightly with the valve seat. 2. The valve spring should be free from damage or rust, must not be tilted, and should have good elasticity ； The length difference of the springs on the same valve disc in the free state should not exceed 1 mm. 3. After the air valve is assembled, the spring force should be even, and there should be no sticking between the valve disc and the spring. 4. After the air valve is assembled, its adjustment mechanism and the opening degree of the valve disc shall comply with the specifications in the drawings. 5. After the gas valve is assembled, a tightness test should be conducted using kerosene; intermittent droplet-like leaks are allowed within 5 minutes, and the extent of such leakage can be referred to in the table below. 6. After assembly, the central bolt and nut of the gas valve should be tightened, with a lock mechanism in place to prevent backsliding. 4.2.9 Packing box, wiper Number of valve disc layers: 1 2 3 4 5 6 Allowed number of leaks per 5 minutes: ≤10 ≤28 ≤40 ≤64 ≤94 ≤130 4.2.9.1 Metal or plastic sealing elements must not have any scratches, damage, or other defects. 4.2.9.2 Before installing the sealing element, it must be ground and fitted so that the planar and radial sealing surfaces make even contact; there should be no less than 5–6 colored dots per square centimeter, with a contact area of at least 80%. 4.2.9.3 The axial clearance of the metal sealing element is 0.05~0.20 mm ； The axial clearance of plastic sealing elements is determined by their coefficient of expansion, and it is generally 2 to 3 times that of metal sealing elements. 4.2.9.4 When assembling the packing seal rings, the opening gaps should be offset from each other. 4.2.9.5 The assembly of sealing elements such as the locking ring and seal ring inside the plastic flat packing box should be carried out in sequence: the locking ring is positioned closer to the cylinder, the seal ring is on the outside, and then comes the flow-blocking ring ； There shall be no chamfers or rounds on the two end faces where the locking ring and the sealing ring meet. 4.2.9.6 When installing the stuffing box, it is necessary to ensure that the lubricating oil and cooling water channels are aligned and unobstructed. 4.2.9.7 The inner cylindrical surface of the oil-scraping ring should fit tightly against the piston rod; the requirements are essentially the same as those for the packing seal ring. During installation, care must be taken to ensure that the cutting edge of the ring is not oriented in the wrong direction. When there are two oil-scraping rings, their cutting edges should be oriented in opposite directions in order to achieve effective scraping of oil back and forth. 4.2.10 Safety Valves 4.2.10.1 The valve body of a closed-type safety valve shall be subjected to a hydrostatic strength test, with the test pressure being 1.5 times the system’s operating pressure. 4.2.10.2 The safety valve shall undergo a gas-tightness test, and the test pressure shall be the system operating pressure. 4.2.10.3 The setting pressure of the safety valve shall be 1.05 to 1.1 times the system’s rated operating pressure.