Pumps and Compressors

Plain Style Reciprocating Compressor Overview

Corken’s plain style reciprocating compressors utilize one set of V-ring packing or, a combination of V-ring and segmented packing per packing rod. Neither of these packing arrangements are oil-free designs. If oil-free gas compression is required, Corken’s D-Style and T-Style compressors are recommended. With the exception of the model D891, all D-Styles are oil free. Since the D891 is not an oil-free compressor, it is used in the same applications as our plain style compressor.

Plain style compressors are typically used in non-toxic, non-corrosive applications where oil-free gas is not required and leakage containment is not critical. LPG (propane & butane), agricultural ammonia, and natural gas applications are where a single packed plain style compressor fits well.

Operating Specifications (Note: Since it is not oil free, the D891 is included with the plain style compressors)

• Piston displacements up to 117 cfm (198.8 m3/hr)
• Working pressures up to 450 psi (31.0 bar g)
• Brake horsepower up to 45 hp (34 kW)
• Maximum outlet temperature: 350 °F (177 °C)

Reciprocating compressors pull vapor into a cylinder through a suction valve by drawing back a piston to create a low pressure area in the cylinder. They pressurize the gas by pushing the piston back up into the cylinder to squeeze the gas out through the discharge valve.

A compressor valve consists of four parts: a seat, bumper, disc and spring. The spring rests against a bumper and pushes the disc against the seat. The disc seals off the flow passage through the seat. If more pressure builds up on the seat side than the bumper side, the disc will be forced away from the seat and gas will flow through the valve.

In order for compression to take place, the piston must be sealed against the wall. This seal is made with several piston rings. To avoid contaminating the process gas with lubricating oils, the piston rings must be made of a self- lubricating material. Corken’s piston rings are usually made of glass-filled PTFE. Gas pressure in the cylinder is used to press the piston ring against the cylinder wall. Ring expanders are used to push the ring towards the cylinder wall so high pressure gas may flow behind the ring.

Piston rings form a good dynamic seal but they are not tight enough to seal all the pressure and gas inside the cylinder; and additional seal is required to do this. This seal is the piston rod packing. The piston rod and packing is a seal that is located at the bottom of the cylinder. It is composed of several parts, the most important being the self-lubricating PTFE V-rings that slightly seal against the piston rod. A spring is included in the packing assembly which allows a slight amount of float to reduce the friction. The rod packing also seals oil in the crankcase out of the compressor chamber to prevent contamination of the gas.

Depending on the type of gas, there will be one to three sets of packing per piston rod. One set of packing controls leakage and oil contamination of the vapor to a satisfactory level for most commercial LP gas and ammonia applications. When leakage and contamination must be held to an absolute minimum, three sets of packing separated by two distance pieces may be utilized. Corken manufactures vertical and horizontal compressors with single, double and triple packing options.

The crankcase converts rotary motion from the motor to reciprocating motion at the piston. With the exception of the model 91, all of Corken’s compressors have an oil pump that pressure lubricates the bearings and wrist pins. The oil pump is a gear type that may be run in either direction. As a result, the Corken compressor may be turned in either direction.

For more information on Corken’s reciprocating gas compressors, click on one of the links below.

Vertical Reciprocating Compressors (Single Packed)

Vertical Reciprocating Compressors (Double Packed Oil Free)

Horizontal Reciprocating Compressors (Single Packed & Triple Packed Oil Free)

Many LPG (propane & butane) and agricultural ammonia piping systems do not provide ideal net positive suction head (NPSH) conditions for liquid pumps. As a result the poor NPSH conditions lead to excessive pump maintenance.

Since reciprocating compressors are only exposed to vapors, they are not affected by poor NPSH conditions. Many LPG and agricultural ammonia pressurized tanks such as railcars and buried tanks have top unloading connections. A reciprocating compressor is the perfect solution for transferring liquids to and from tanks of this type.

Our plain style vertical reciprocating compressor line is a single packed compressor and does not offer oil-free gas compression. This packing configuration is typically used in non-corrosive, non-toxic applications where oil-free service is not required and leakage containment is not critical. Plain style compressors are commonly used in propane, butane, agricultural ammonia, and natural gas applications. If oil-free compression and leakage containment are critical, we recommend using one of our D- or T-Style designs. A D-Style compressor has two sets of V-ring packing while the T-Style has three sets. Most propane, butane and agricultural ammonia applications only require a plain style compressor.

To find a plain style reciprocating compressor for your application, refer to the information listed below. If your propane, butane or agricultural ammonia application requires oil-free gas compression or a higher level of containment, you can review our D- and T-Style designs.

Plain Style Reciprocating Compressor

• Plain style reciprocating compressors utilize one set of V-ring packing per piston rod and do not have a distance piece
• Plain style configurations are not oil-free designs
• Typically used in non-toxic, non-corrosive applications where oil-free gas is not required and leakage containment is not critical
• If oil-free gas compression is required, a D-Style or T-Style vertical compressor is recommended

Operating Specifications

• Piston displacements up to 117 cfm (198.8 m3/hr)
• Working pressures up to 450 psi (31.0 bar g)
• Brake horsepower up to 45 hp (34 kW)
• Maximum outlet temperature: 350 °F (177 °C)

Learn More >>

Unloading multiple tank cars can present challenges for the plant designer and operator. Selecting the correct reciprocating gas compressor and designing a proper piping system can make the daily operations of a plant very efficient. However, if done incorrectly, it can create operational issues that are difficult and expensive to resolve.

Large scale unloading operations can see significant benefits from certain design parameters incorporated at the plant design stage. Many details are specific to the particular location, product being unloaded, owner’s preferences, etc. However, some general guidelines can be applied to nearly all multiple tank car unloading applications.

Two such guidelines are the proper selection of the gas compressors, and the method of vapor pipe routing. At Corken, we have been building tank car unloading compressors since the 1940s. Our experienced application engineers can help you select the correct compressor for the job. The following pages show some general guidelines for selecting the correct compressor and properly routing the vapor piping.

Issues With Unloading Multiple Tank Cars

Any flowing fluid will take the path of least resistance. When using a single, long vapor header as shown in the diagram below, tank cars 1 and 2 will empty first since they have the shortest vapor and liquid lines. Short vapor and liquid lines have less resistance so the flow rate is higher and unloading times are faster. This is when the issues begin. When tank cars 1 and 2 have emptied the liquid, the high pressure vapor from the compressors then has a direct path to the liquid line. When this happens vapor will flow directly to the liquid header and the unloading process for the remaining tank cars will be slowed significantly or even stopped.

Solutions For Unloading Multiple Tank Cars

The capacity of one Corken model 891 compressor is well suited for unloading two typical 33,000 gallon tank cars simultaneously. Using a dedicated model 891 compressor for each pair of tank cars eliminates the issues related to using a single long vapor header. For example, when tank cars 1 and 2 empty the liquid, it has no effect on tank cars 3 and 4 since they are unloaded by a different compressor using separate vapor piping.

In any tank car unloading application, it is best to locate the compressor as close as possible to the tank car. This minimizes the distance from the compressor to the tank car and reduces the energy loss (heat loss) of the compressor’s discharge gas. Using one model 891 per two tank cars works well with this rule since the compressors can be spaced evenly along the rail spur.

Using a single vapor header with isolation valves (as shown in the diagram) allows redundancy in the system. For example, if compressor 3 goes down for routine maintenance, either compressor 2 or 4 could be used to unload tank cars 5 and 6.