Steam reciprocating pump

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Reciprocating pumps belong to positive displacement pumps. It is used in production to transport liquids with high pressure, or various liquids that are highly viscous, corrosive, flammable, explosive, or highly toxic. Especially when the flow rate is low, the advantages of this pump become even more evident; the optimal operating range is a flow rate of less than 100 m3/h and a pressure of over 100 MPa. Structure and principle of steam reciprocating pumps: Steam reciprocating pumps use steam at a certain pressure to drive the piston to move back and forth. The piston rod of its power cylinder is directly connected to the piston rod of the pump cylinder, moving back and forth together. A steam reciprocating pump consists of a pump cylinder, a cylinder, and connecting parts. The pump cylinder section consists of the pump cylinder, piston, suction valve, discharge valve, and piston rod sealing device, among other components. The cylinder is the power part of the pump, and it consists of a cylinder, a piston, and valve gears. The connecting part consists of a rocker arm, tie rod, connector, etc. The cylinder piston and the pump cylinder piston are connected together by a connector, enabling the pump cylinder piston to undergo the same stroke as the cylinder piston. The valve gear and the cylinder piston are connected through tie rods and rocker arm brackets, allowing the valve gear to operate in coordination and ensuring that steam can be continuously distributed to both sides of the cylinder, thereby driving the piston to move back and forth. 1.1 Disassembly and inspection of steam reciprocating pumps: 1. Disassembly: ① Disconnect the cooling water pipes and check for corrosion ； ②Disassemble and inspect the oil filler, oil pipelines, and accessories ； ③Disassemble the pulling mechanism and check the wear condition of various transmission components ； ④Disassemble the steam and liquid cylinders, and check the wear condition of the sleeves, pistons, piston rods, piston rings, etc ； ⑤Remove and inspect the packing ； ⑥Remove the inlet and outlet valves of the cylinder, and check the wear condition of the valve seats, valve caps, valve stems, etc ； ⑦Disassemble the valve train to check the wear condition of the valve plates and tie rods ； 2. Maintenance of the cylinder in steam reciprocating pumps: Before disassembling a steam reciprocating pump, it is necessary to drain all condensate and residual liquid from the cylinder. During disassembly, the following two points should be noted: (1) When removing the piston rings, special tools must be used to prevent them from breaking. (2) When removing the valve plates, proper markings must be made to avoid any confusion. (3) The inner surface of the cylinder must be smooth and free of cracks; its internal diameter’s ovality and taper must comply with the values specified in the table below:
Internal diameter of cylinder | Maximum increase in diameter | Installation requirements | Wear limit | Ovality | Taper
<100 | 1.5 | 0.03 | 0.06 | 0.6 | 0.3
100–150 | 1.5–2.0 | 0.04 | 0.08 | 0.7 | 0.4
150–300 | 2.0–3.0 | 0.04 | 0.08 | 0.8 | 0.4
300–400 | 3.0–4.0 | 0.05 | 0.1 | 0.9 | 0.5
400–500 | 4.0–5.0 | 0.05 | 0.11 | 0.7 | –
Unit: mm
(4) The ovality and taper of the piston must also conform to the values given in the table below:
Piston diameter | Installation requirements | Wear limit | Ovality | Taper
<200 | 0.04 | 0.03 | 0.2 | 0.2
200–400 | 0.05 | 0.04 | 0.3 | 0.3
(5) The clearance between the cylinder and the piston must meet the criteria outlined in the table below:
Cylinder diameter | Installation clearance | Replacement clearance
<50 | 0.25 | 0.8
50–75 | 0.25 | 0.8
75–100 | 0.31 | 2.5
100–125 | 0.35 | 1.3
125–150 | 0.41 | 1.5
150–200 | 0.45 | 1.7
200–250 | 0.52 | –
250–300 | 0.55 | 2.4
300–350 | 0.62 | 2.8
350–400 | 0.73 | 3.4
(6) When installing piston rings on the piston, their openings must be staggered relative to each other. Their thickness should be 0.5–1 mm less than the depth of the groove. Piston rings must be free of defects such as sand holes or air bubbles and must possess sufficient elasticity. The installation clearance must comply with the values given in the table below:
Cylinder diameter | Installation clearance for piston rings | Replacement clearance for piston rings
<100 | 0.6 | 0.04–0.06 | 2.5 | 0.15
100–125 | 0.8 | 0.04–0.06 | 3 | 0.15
125–150 | 1 | 0.05–0.07 | 3.5 | 0.15
150–200 | 1.2 | 0.05–0.07 | 4 | 0.15
200–250 | 1.4 | 0.06–0.09 | 4.5 | 0.2
250–300 | 1.6 | 0.06–0.09 | 5 | 0.2
300–350 | 1.8 | 0.07–0.10 | 5.5 | 0.2
350–400 | 2 | 0.07–0.10 | 6 | 0.2

3. Inspection and repair of the drive mechanism in steam reciprocating pumps:
(1) Drive mechanism: If the components of the drive mechanism do not fit together properly or if they are excessively worn, the pump’s stroke will become uneven during operation. Therefore, during maintenance, it is essential to check their clearances:
① The fit between the center support bushing and the rocker arm shaft should be H9/f9.
② The fit between the connecting rod bushing and the pin connecting the connecting rod to the cylinder should be H7/f6.
③ The fit between the connecting rod bushing and the pins at both ends of the connecting rod should also be H7/f6.
(2) Valve mechanism: For flat-type valve plates, use the coloring method to check how well the valve plate contacts the valve seat surface. If contact is poor, grinding is required to ensure that both surfaces are smooth; the contact area should be no less than 2–3 points per square centimeter. The maximum wear amount of the steam distribution tie rod can be referenced to that of the piston rod. The surface and threaded portion of the steam distribution rod should be free from any damage or wear, and the nut should fit tightly without being loose. 4. Inspection of the cylinder: The surface of the cylinder liner should be smooth, without any cracks, pores, grooves, or other defects. The maximum allowable depth of wear grooves must not exceed the values specified in the technical requirements. If it does exceed these limits, corrective measures or boring of the cylinder is necessary.
① The surface of the piston should also be smooth, without cracks, pores, or grooves. Its cylindricity must meet the technical requirements; if it exceeds the limits, the piston must be repaired or replaced.
② The clearance between the cylinder and the piston must comply with the technical specifications.
③ The end clearances at both ends of the piston within the cylinder must also meet the technical requirements.

(6) Piston rings:
① Piston rings must be free from pores and defects; their elasticity must be sufficient.
② The thickness of piston rings for hydraulic cylinders should be less than the depth of the piston groove, which ranges from 0.5 to 1.5 mm. The installation positions of the piston rings must be offset by 120° relative to each other.
③ There must be no longitudinal grooves on the surface of the piston rings; they must make good contact with the cylinder wall. A feeler gauge measuring 0.05 mm must not be able to fit between them.
④ The installation clearances for piston rings in air and hydraulic cylinders must conform to the following table:

| Cylinder diameter | Installation clearance | Maximum wear clearance | Butt joint clearance | Groove-side clearance |
|-------------------|------------------------|------------------------|----------------------|-----------------------|
| <100 | 1–1.6 | 0.06–0.08 | 3.8–4 | 0.2 |
| 100–125 | 1–1.9 | 0.06–0.08 | 3.8–4 | 0.2 |
| 125–150 | 1.2–2.4 | 0.06–0.08 | 4.5–6 | 0.2 |
| 150–200 | 1.6–3.1 | 0.07–0.10 | 5–6 | 0.2 |
| 200–250 | 2–3.8 | 0.07–0.10 | – | 0.3 |
| 250–300 | 2.5–4.5 | 0.07–0.10 | – | 0.3 |
| 300–350 | 2.6–5.8 | 0.1–0.12 | – | 0.3 |
| 350–400 | 3–6 | 0.1–0.12 | – | 0.3 |

(7) Valve inspection:
① The contact surfaces between the valve cover and the valve seat must be smooth and airtight. Using a dye test, it should be confirmed that there is continuous circular contact; any gaps are unacceptable.
② If the mass of the valve cover differs from its original value by more than the permitted limit, it must be replaced.
③ There must be no corrosion, pitting, damage, or severe radial grooves on either the valve cover or the valve seat.
④ The number of spring coils, their height, and elasticity must all meet the technical requirements.
⑤ The lifting heights of the valve covers must be equal; any deviation must not exceed 5%.
⑥ The valve covers must be concentric with the valve seat holes; the fit between them must be H9/c9 or H9/d9.
⑦ The valve seat must be securely and tightly mounted onto the pump body.

Percentage difference in original weight of valve plates:
| Percentage difference | Description |
|-----------------------|---------------------------------|
| <0.5 | 80–85 |
| 0.8–1.3 | 5.6 |
| >1.3 | 6.5 |