Reciprocating Compressor Parts: A Simple, Yet Useful Guide

Compressors that are used in the gas, chemical, and petrochemical industrial processes are made of several components, each of which offers some level of support to the machine. These components have a role to play either in managing heat, aiding in rotation, enhancing the machine’s durability, narrowing gas flow, and even enabling other parts to carry out their task efficiently. In this article, Linquip has compiled useful information on reciprocating compressor parts. So read this new blog and drown yourself in learning!

Different Reciprocating Compressor Parts

Let’s get into knowing different reciprocating compressor parts to get an overall idea of their applications within the compressor.

1. Frame

The frame is a heavy, rugged housing containing all the rotating parts and on which the cylinder and crosshead guide is mounted. Compressor’s manufacturers rate frames for a maximum continuous horsepower and frame load.

Separable compressors are usually arranged in a balanced-opposed configuration characterized by an adjacent pair of crank throws that are 180 degrees out of phase and separated by only a crank web. The cranks are arranged so that the motion of each piston is balanced by the motion of an opposing piston.

2. Cylinders

Cylinders are pressure vessels that contain the gas that is to be compressed, and as such, they are one of the most important components of a reciprocating compressor. Single-acting cylinders compress gas in only one direction of piston travel. They can be either head end or crank end. Double-acting cylinders compress gas in both directions of piston travel. Most reciprocating compressors use double-acting cylinders.

The function of cylinders as reciprocating compressor parts is to cool the temperature of the machine during its compression cycle which tends to generate heat. This becomes possible with the use of a water jacket or fins in the cylinder which provides cooling air.

Watch Video about reciprocating compressor parts

3. Distance Piece

The distance piece provides separation between the compressor cylinder and the compressor frame. Distance pieces can be contained in either a single- or double-compartment arrangement. In the single-compartment design, the space between the cylinder packing and the diaphragm is lengthened so that no part of the rod enters both the crankcase and cylinder stuffing box. Oil migrates between the cylinder and the crankcase. If oil contamination is a concern, an oil slinger can be provided to prevent packing lube oil from entering the compressor frame. For toxic service, a two-compartment design may be used. No part of the rod enters both the crankcase and the compartment adjacent to the gas cylinder.

4. Piston

The mode of operation of the compressor greatly relies on the piston. This is because the piston is the component that actually compresses air. It also moves the energy from the crankcase to the gas contained in the cylinder in a bid to prevent the refrigerant from leaking through the gap. In between the piston and cylinder walls, this component is usually covered with piston rings.

It is normally located at the end of the piston rod and acts as the movable barrier in the compressor cylinder. Selection of material is based on strength, weight, and compatibility with the gas being compressed. The piston is usually made of a lightweight material such as aluminum or from cast iron or steel with a hollow center for weight reduction.

5. Piston Rings

The piston rings are wounded on the piston and as the piston moves up and down the cylinder, the piston rings come in contact with the walls of the cylinder. Due to the amount of friction created during this reciprocating motion, rings have to be replaced frequently in order to maintain the seamless operation of the compressor. In some cases, a wear band or rider ring is used as an additional piston ring.

The function of rider ring as the reciprocating compressor parts is to reduce the probability of wear and tear occurring between the cylinder and piston. While rings have to be softer than the liner wall and cylinder, different types of rings can be used for the piston which are metallic rings and non-metallic rings.

6. Cross Head

A crosshead enables the piston to be inserted in the cylinder bore. The use of a crosshead enables a compressor to use a narrow piston and it enables longer strokes and higher efficiency.

7. Crankshaft

The crankshaft rotates around the frame axis and drives the connecting rod, piston rod, and piston.  This component is used in large compressors that operate above 150 kW. Crankshafts as reciprocating compressor parts are either connected to the electric motor directly or indirectly with the use of a belt and pulley system. As the motor shaft rotates, the crankshaft also performs a rotary motion which gives the piston the ability to carry out its reciprocating motion inside the cylinder. But first, a rod has to be connected to the crankshaft and rod to enable the piston to perform an upward and downward movement.

8. Connecting Rod

A connecting rod, also called a con rod, is the part of a piston engine which connects the piston to the crankshaft. Depending on the power which the machine operates, a forged steel connecting rod or ductile iron material can be used. The former is in compressors that operate above 150 kW, while the latter finds use in compressors that work around 150kW or less. The physical connection has one side of the rod linked to the piston using a piston pin. Alternately, the other side of the rod is connected to the crankshaft using a connecting cap rod.

While the connection may sound simple, it is what is required to give the crankshaft its rotary motion which also helps the piston to translate within the cylinder. Therefore, the connecting rod changes the rotary motion to reciprocating motion.

9. Valve

The essential function of compressor valves is to permit gas flow in the desired direction and to block all flow in the opposite direction. Each operating end of a compressor cylinder must have two sets of valves. The set of inlet (suction) valves admits gas into the cylinder. The set of discharge valves is used to evacuate compressed gas from the cylinder.

The valves as reciprocating compressor parts are also of various configurations. These include:

• Ring valve
• Poppet valve
• Plate valve

10. Bearings

Bearings located throughout the compressor frame assure proper radial and axial positioning of compressor components. Main bearings are fitted in the frame to properly position the crankshaft. Crank pin bearings are located between the crankshaft and each connecting rod. Wrist pin bearings are located between each connecting rod and crosshead pin. Crosshead bearings are located at the top and bottom of each crosshead.

Most of the bearings as reciprocating compressors parts are hydrodynamic lubricated bearings. Pressurized oil is supplied to each bearing through oil supply grooves on the bearing surface. The grooves are sized to ensure adequate oil flow to prevent overheating.

So this is all you need to know about reciprocating compressor parts and their application within a compressor. If you enjoy this article and want to share your experience with different compressor parts in Linquip, let us know what you think by leaving your idea in the comment section. Is there any question we can help you with? Feel free to sign up on our website where our experts waiting to give you the professional advise you need.

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