What Is a Piston Compressor?

A piston compressor is a compressor that relies on the reciprocating movement of a piston to pressurize and transport gas. It is a positive displacement compressor, also known as a "reciprocating piston compressor" or "reciprocating compressor". It is mainly composed of working cavity, transmission parts, fuselage and auxiliary parts. The working cavity is directly used to compress the gas, and is composed of a cylinder, a cylinder liner, a valve, a packing, a piston and a piston rod. The piston is driven by the piston rod to reciprocate in the cylinder. The volume of the working chamber on both sides of the piston changes in reverse. The gas on the side with the reduced volume is discharged through the valve due to the increase in pressure, and the gas on the side with the increased volume passes through the gas due to the decrease in pressure The valve sucks in the gas, and the transmission parts are used to realize the reciprocating motion. There are crankshaft connecting rod, eccentric slider, swash plate, etc. Among them, the crankshaft connecting rod mechanism is most commonly used. It consists of a crosshead, a connecting rod and a crankshaft. ^[1]

After the motor is started, the crankshaft rotates. Through the transmission of the connecting rod, the piston reciprocates. The working volume formed by the cylinder inner wall, the cylinder head and the piston top surface will change periodically. When the piston starts to move from the cylinder head, the working volume in the cylinder gradually increases. At this time, the gas is pushed along the intake pipe to open the intake valve and enters the cylinder. Until the working volume reaches the maximum, the intake valve is closed. ; When the piston moves in reverse, the working volume in the cylinder decreases and the gas pressure rises. When the pressure in the cylinder reaches and is slightly higher than the exhaust pressure, the exhaust valve opens and the gas is discharged from the cylinder until the piston moves to the limit position. The air valve is closed. When the piston moves in the opposite direction again, the above process repeats. In short, the crankshaft rotates once, the piston reciprocates once, and the processes of intake, compression, and exhaust in the cylinder successively complete a working cycle. ^[2]

The piston compressor is mainly composed of the body, crankshaft, connecting rod, piston group, valve, shaft seal, oil pump, energy regulating device, oil circulation system and other components.

Body : including

In terms of structure, piston compressors are often divided into the following types according to the relative position of the centerline of the cylinder.

(1) Vertical compressor

The centerline of the cylinder of the vertical compressor is perpendicular to the ground. Because the working surface of the piston does not bear the weight of the piston, the abrasion of the cylinder and the piston is small, and the working conditions of the piston ring are improved, which can extend the service life of the machine. The load of the vertical compressor mainly generates tensile and compressive stress on the fuselage, and the fuselage is simple in force, so the fuselage is simple in shape, light in weight, and difficult to deform. The reciprocating inertial force acts vertically on the foundation, the size of the foundation is small, and the footprint of the machine is small.

(2) Horizontal compressor

The centerline of the cylinder of the horizontal compressor is parallel to the ground, and is divided into single or double rows, and all are on one side of the crankshaft. Because the entire machine is within the operator's line of sight, it is easy to manage and maintain, and it is easier to install and remove the crankshaft and connecting rod.

(3) Angle compressor

The centerlines of the cylinders of the angular compressor are at a certain angle to each other, but not equal to 180 °. Due to the different positions of the cylinder centerlines, they can be divided into L-shaped, V-shaped, W-shaped, and fan-shaped. The structure is convenient for installation and disassembly of air valve, interstage cooler and interstage air duct, compact structure and good dynamic balance.

(4) Opposed compressor

The cylinders are arranged horizontally on both sides of the crankshaft, and the offset angles of two adjacent rows of cranks are not equal to 180 °. There are two types of opposed compressors: one is that the centerlines of the two opposite rows of cylinders are not in a straight line, and are made into odd rows such as 3, 5, 7, and so on; , Into even columns.

(5) symmetrical balance compressor

Between the two main bearings of the symmetrical balance compressor, the crank angle of the two rows of cylinders is 180 °. The inertia force can be completely balanced and the speed can be increased. The piston forces of the opposite rows can cancel each other, reducing the stress and wear of the main journal . In the multi-row structure, the number of cylinders in each row is less, the installation is convenient, and the product deformation is easier than the horizontal and vertical. ^[3]

Advantages of piston compressors:

A wide range of applicable pressures, piston compressors can be designed for low pressure, medium pressure, high pressure and

The selection of the compressor can be summarized as follows: First, the selection of the technical parameters of the compressor, which includes the adaptability of the technical parameters to the chemical process and the advanced nature of the technical parameters themselves. The second is the choice of the compressor's structural performance, which includes the choice of the compressor's structural type, performance and adaptability to working conditions, which affects the economical operation of the compressor. Okay. The general principles of compressor selection are both applicable and economical, safe and reliable, and easy to maintain.

The compressor should first meet the process requirements, mainly in the following aspects.

(1) Compressed media put forward requirements on the compressor, including whether a small amount of leakage of the medium is allowed, whether it is allowed to be contaminated by lubricants, and the exhaust temperature is limited;

(2) the displacement of the compressor;

(3) the inlet and outlet pressure of the compressor.

Under the premise of meeting the following process requirements, if there are several types or types of compressors to choose from. Determined after further comparison of various compressor types.

The requirements for the selection of compressors in the chemical industry and petrochemical industry are as follows.

(1) Security issues

Chemical, petrochemical compressed gas, if it is flammable, explosive or corrosive,

1) Minor repairs

Minor repairs to compressors generally include the following:

(1) Check and tighten all connecting bolts and crosshead pins (including anchor bolts).

(2) Check and remove the coke and dirt on the valve parts.

(3) Check or replace the valve plate, spring, valve seat and lift limiter.

(4) Check or replace the stuffing box seal.

(5) Inspect and repair lubrication systems such as oil injectors, check valves, lubricating oil filters, tubing joints, etc.

(6) Check and adjust the transmission belt or coupling.

Generally speaking, minor repairs to compressors are targeted, often repairing the failure of a certain part of the compressor, such as a consumable gas valve. Should pay attention to observation at any time, and replace it in case of failure.

2) Intermediate repair

Intermediate repair of compressors generally includes the following:

(1) Including minor repairs.

(2) Remove the dirt in the air chamber and water jacket, and measure the wear of the inner wall of the cylinder.

(3) Inspect, repair or replace the piston, piston ring, guide ring and piston rod.

(4) Check and scrape the size of the connecting rod, investigate the gap or replace it.

(5) Check and adjust the clearance on the upper point of the piston.

(6) Inspect, repair or replace all pressure gauges, thermometers, safety valves and circulation valves.

(7) Check, clean or replace the check valve.

(8) Check and clean the cooling water system.

(9) Change the lubricant.

3) Overhaul

Overhauling a compressor generally includes the following:

(1) Including the intermediate repair content.

(2) Disassemble and clean the entire compressor.

(3) Check the wear of crosshead components, crankshaft components, crosshead slideways, and repair or replace if necessary.

(4) Correct the center and level of each component.

(5) Check, repair or replace each cooler and separator, and perform water pressure and air tightness tests if necessary.

(6) Inspection of crankshaft, crosshead pin, connecting rod, connecting rod bolt and piston rod.

(7) Check and adjust flywheel runout.

(8) Inspection and repair foundation.

(9) Anticorrosive treatment and painting.

The above is the basic maintenance of the compressor. During the actual maintenance of the factory, it can be appropriately increased or decreased according to the condition of the machine being repaired. ^[6]