Understanding Valve Materials for Reciprocating Compressors
Reciprocating compressors are composed of various parts necessary to compress the gas. One of the most crucial components is the valve. Continue reading for an analysis of valve materials.
Reciprocating compressors are used extensively across a wide range of industries. Reciprocating compressors are composed of several moving components that work together to compress the gas. One of these vital components is the compressor valve. This article concerns the valve materials that make compressor valves durable and suitable.
A reciprocating compressor’s primary job is to compress gas using pistons and ensure the delivery of the compressed gas to its destination. This machine is also known as a ‘piston compressor.’ Reciprocating compressors power several industrial tools and applications, making them versatile and durable.
The Compressor Valve
Compressor valves generally consist of 4 distinct parts:
The spring rests head to head with a guard and pushes the disk against the seat. This disc is positioned so that it is off the flow passage via the seat. If the pressure on the seat side builds up more than on the guard side, the disc will automatically be forced away from the seat. This allows gas to flow through the valve.
Compression can only occur if the piston is adequately sealed against the wall. The seal is composed of several piston rings. The piston rings need to be made of self-lubricating materials to prevent the contamination of the process gas with lubricating oils.
Compressor Valve Materials
The materials used for constructing compressor valves are always carefully selected for compatibility with the gas to be compressed and long-term operation or durability. However, these materials don’t necessarily have to be entirely resistant to corrosion to the process fluid, as long as they can be contaminated.
If some contamination of the process fluid is acceptable, the valve materials may be permitted to be attacked. But if the purity of the process fluid is paramount, then the materials used in making the valves must be resistant to corrosion. The corrosion rate of the operation will significantly determine the useful life span of the compressor valve.
To extend the life span of a compressor valve, allocating an erosion or corrosion allowance of sacrificial material is possible. However, this will only occur when the operating temperature/pressure is below the rated temperature/pressure.
As soon as the corrosion allowance has been utilized, the compressor valve must be refurbished or replaced immediately because an extreme operating environment might also warrant an erosion allowance/external corrosion.
Other Valve Materials
Valve plates are usually made from a wide range of stainless steel and thermoplastics for effective operations. Several spring materials are available, including Inconel X-750(a nickel-base alloy with iron and chromium), music wire, 302 stainless steel, etc. Other materials used for making compressor valves include:
- Carbon steel
- Grey cast iron
- Nodular iron
- High tensile steel
- SG iron
- Ductile iron
- Ni-Resist iron
- Austenitic stainless steels
- Higher steel allows
- Nickel alloys
Other super alloys that serve as materials for fabricating compressor valves include Haynes 25 and Elgiloy, which are often used to prevent spring hydrogen embrittlement.
Selecting the materials for constructing compressor valves can be a complicated process. It often leads to compromises to avoid galvanic or galling corrosion.
Compressor valve manufacturers have broad experience determining the best materials for solving application issues. This is why the choice of materials for fabricating compressor valves is best left to them.
The 3 Types of Valves in Reciprocating Compressors
Reciprocating compressors typically utilize one of these spring-located, gas-actuated valve configurations:
Ring Type Valve
As its name suggests, the ring-type valve consists of concentric ring valves that use one or more reasonably narrow rings carefully arranged concentrically around the center line of the compressor valve. These valves have low-stress benefits, which can be chalked up to the considerable reduction of stress concentration points.
However, the ring-type valve has one significant drawback: maintaining uniform flow control across this compressor valve can be challenging.
This is why ring-type valves are recommended for 60 MPa discharge pressure or 30 MPa differential and 600 rpm.
Plate Type Valve
The plate-type valve is somewhat similar to the ring-type valve, i.e.; it contains several concentric rings of valve plates. The concentric ring valve plates are one element. The primary benefit of the plate-type valve is the heightened control over flow since the valve plate is made of a single element.
The single element also implies that the previously available edges designed for impact are minimized. Moreover, this type of valve design permits the use of damping plates.
The primary drawback or disadvantage of the plate-type valve is its geometric use, which can result in higher stress concentrations in the long run.
Moreover, the stress on the valve plate is higher than observed with the poppet-type valve (discussed next). Therefore, the plate-type valve is widely used in reciprocating compressors that handle oil-free gases.
Poppet Type Valve
The poppet-type valve comprises several sealing elements and more than one same-sized port. It is used in low-speed reciprocating compressors and gas that contain oil particles. This is a high-lift valve; the pressure drop across the poppet-type valve is low due to this.
This type of compressor valve’s primary advantage is its streamlined shape and high flow efficiency, as well as its intolerance of uneven flow distribution.
The poppet-type valve functions exceptionally well when utilized within medium-pressure ranges. It is usually found and used extensively in reciprocating compressors in the hydrocarbon field due to easy maintenance.
The reciprocating compressor is one of the most versatile machines used extensively in several industrial processes. It compresses gas using pistons and comprises more than a few components. Valves are crucial compressor components that must never be taken for granted.
This is why it is crucial to understand the valve materials used. This makes it easier for the technician or mechanic handling maintenance processes to pick the most suitable compressor valve when replacing a defective or damaged compressor valve.
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