When it comes to gas, chemical, petrochemical, and other industrial processes, reciprocating compressors play a major role. These compressors are the most well-known and widely used compressors involving positive displacement based on a specific set of basic parts. So, what are these reciprocating compressor parts and what do they do?
What is a reciprocating compressor?
Reciprocating compressors are positive-displacement devices that work on a reciprocating principle in order to deliver gas at high-pressures.
This motion is enabled within the device using pistons. Generally, reciprocating compressors can be divided into two types: Integral (low speed) and Separable (high speed).
In the natural gas industry, large reciprocating engines are used to supply high-pressure gas for well drilling, generate low-pressure plants, and move natural gas through the pipeline.
11 Types of Reciprocating Compressor Parts
Reciprocating compressors are made up of multiple parts. Below, we discuss these reciprocating compressor parts, and their importance in each compressor.
1. Cylinders
Reciprocating compressor parts include cylinders. These cylinders found in process industries are separable from the frame, accommodating both discharge and suction valve plates.
Small, higher-pressure cylinders and typically crafted from steel, while larger, low-pressure cylinder are constructed from cast iron. In other cases, ductile iron can be used, although steel is the most desirable in the hydrocarbon service.
To prove a renewable surface and prevent excessive wear on the cylinder, most are equipped with replaceable liners. This removable surface prevents the cost of replacing a complete cylinder when the unit has been scored.
Industrial industries may also equip cylinders with cooling to reduce temperatures found in the compression cycle, often by means of a water jacket.
2. Piston
The piston is often referred to as the heart of the reciprocating compressor.
Generally crafted from low-weight materials such as aluminum, aluminum alloys to reduce rod load and shaking, and the piston is responsible for the translation of energy to the gas in the cylinder from the crankcase.
To avoid leakage, the piston is often equipped with sliding self-lubricating seals, also known as piston rings. These rings also help to avoid wear and increase efficiencies through the reduction of friction force.
3. Piston Rod
Threaded through the piston, the piston rod is responsible for transmitting the reciprocating crosshead into the piston.
This component is traditionally manufactured out of alloy steel. Where it is passed through the cylinder packing, the surface must be polished and hardened.
Limits set forth by the compressor vendor must be maintained to avoid premature wear, reduced efficiency, higher leakage, and raised maintenance expenses.
4. Distance Piece
This separable housing is the piece that connects the cylinder and the frame. The distance piece may contain multiple compartments and it may be open or closed, extra long, single, or double.
The purpose of these reciprocating compressor parts is to isolate the rod that is entering the crankcase and receive lubrication from the cylinder that is in contact with the gas.
This step is very important because it prevents contamination and maintains synthetic lubricant in the cylinder.
5. Rod Packing
Similar to the piston rod, rod packing is essential to preventing gas leakage as it is passed through the cylinder and crank closure. Where a cooling pack is needed, stuffing boxes may be jacketed for liquid coolant.
Packing rings sit at the heard of the rod packing assembly. These main types are:
- Backup ring
- Pressure Breaker for Radial ring
- Tangent ring
6. Crankshaft
Reciprocating compressors above 150 kW (200 hp) are typically comprised of crankshaft forged out of steel.
In order to compensate of reciprocating and rotary unbalance, each crankshaft should have a removable balance weight. However, when over 800 rpm the crankshaft should be dynamically balanced.
7. Bearing
The connecting and main rod bearings should be steal-backed and split-sleeved.
Antifriction bearings can only be used in compressor components that are rated lower than 150 kW.
8. Connecting Rod
Similarly to crankshafts, connecting rods are used in compressors that are above 150 kW (200 hp).
Also manufactured out of forged steel, the connecting rod also has a drilled hole to allow for the passage of oil. This component connects the crosshead and crankshaft, converting a rotary motion into a motion that is reciprocating.
9. Cross Head
Each and every industrial-grade reciprocating compressor comes completed with a Crosshead.
This component is used to guide pistons into the cylinder bore. Due to this, it permits a greater capacity and longer strength while allowing a heightened control of oil carryover into the cylinder.
10. Valve
Perhaps one of the most essential reciprocating compressor parts are the gas-actuated, spring-located valves. In general, one of these three valve configurations are used:
- Plate Type valve – Compared to concentric ring valves, plate valves are similar besides the fact that they are joined in a single element. The advantage to this valve type is the heightened control over flow. The single element means that the edges previously available for impact are reduced. Furthermore, the design permits the use of damping plates. The disadvantage are it’s geometric use which has the potential to lead to higher stress concentrations.
- Poppet Type valve – This type of valve is comprised of sealing elements and more than one same-sized ports. Advantages include high flow efficiency and streamlined shape. This valve works best with medium temperature ranges and is popularly found in the hydrocarbon field.
- Ring Type Valve – Just the name suggests, the ring type valve consist of concentric ring valves. These valves have a low-stress advantage, which can be attributed the reduction of stress concentration pint. The only disadvantage here is the difficulty to maintain uniform flow control.
11. Lubrication System
Both medium and heavy-duty compressors require force type lubrication.
The main component here is the lube oil tank, pressure regulating valve, lube oil cooler, dual oil filter, main oil pump, and associated accessories.
Conclusion
Reciprocating compressors work to transport natural gas from the suction manifold and into the natural gas cylinder, which is also referred to as the compression cylinder.
An internal combustion engine powers this entire process. When the compressor’s operating life increases, then the packing systems and rings will wear out resulting in higher leaks. Therefore, high quality components and expert installation are the key to ensuring balance in this essential system.
The major components of industrial type reciprocating compressor parts are:
- Compressor valves
- Bearings
- Piston
- Crankshaft
- Distance piece
- Frame
- Cylinder
If you would like to find out more information about reciprocating compressors, contact an expert.