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Increase In Rod Packing Life | Factors Affecting Liquid Cooled Case Efficiency | Heat Sources | History Of Liquid Cooled Case | Liquid Cooled Case Design Requirements | Aavolyn TY655 Fab Cup Design | Packing Cup Purpose | Gasket Cup Design | Coolant Passage Design | Gas Compressor Institute Liberal, Kansas April 2010

PROCESS COMPRESSOR SERVICE

  

INCREASE IN ROD PACKING LIFE

The purpose of a liquid cooled packing assembly versus a non-liquid cooled assembly is to remove heat from the sealing area and thus increase the life of the packing rings.

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Aavolyn TY655 Fab Cup
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Aavolyn TY655 Fab Cup
 

FACTORS AFFECTING LIQUID COOLED CASE EFFICIENCY

  • Coolant Inlet Temp
  • Size of surface area for heat transfer
  • Distance of cooling flow to heat source
  • Flow rate of coolant

In all sealing applications, one of the major limitations to extended seal life is the heat the seals are exposed to during operation. This sealing surface is normally a shaft or cylinder wall.

With the use of filled Teflon® and other thermoplastics in the sealing cups, heat becomes more of a problem. Each filled Teflon® has a specific PV limit which is a combination of pressure and temperature. For more information on PV limits, contact our Engineering department and they will assist you with your particular application in the field.

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HEAT SOURCES

  • Operating Temperature
  • Operating Pressure
  • RMS finish of sealing surface
  • Physical properties of sealing material
  • Lubrication
  • Properties of gas or liquid to be sealed
  • Stroke and RPM
  • Compression Ratio
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AAVOLYN Expo Booth
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AAVOLYN Expo Booth
 

HISTORY OF LIQUID COOLED CASE

With the increase of discharge pressures in reciprocating compressors, additional temperatures were experienced in the packing case area. The frictional heat generated at the rod surface began to affect the performance of the seal rings. It was determined that cases used in pressures over 500 PSI in non‐lube service required cooling and 5000 PSI in lube. To remove excess heat from inside the case. The first water-cooled cases were cooled externally using grooves between the packing cups and a flow system between the grooves. Coolant was introduced and circulated to absorb heat and remove it from the packing case. This style was soon replaced by internal designs because of the distance of the cooling from the rod area. Liquid cooling became even more important when non‐lubricated compressors were developed. Current API specifications now require internally cooled packing cases on all non‐lube compressors.

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Liquid Cooled Design
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Liquid Cooled Design
 

LIQUID COOLED CASE DESIGN REQUIREMENTS

To ensure you obtain maximum heat removal in the cooled packing case, certain design features must be incorporated. A flow pattern for the cooling liquid must be established so that all areas of the cooled cups receive flow under pressure. Coolant enters at the lowest level and flows back toward the gasket cup which is the highest source of heat. Then the coolant is circulated forward. The coolant must enter each cooling cup lower than when it flows out. This keeps pressure on the coolant to continue moving and removing heat effectively from the packing area.


ASSEMBLY

A liquid cooled case must be always looked at as an assembly. Before installing in the compressor, it should be tested to ensure that the cooling system is without leaks. Air can be applied to the coolant inlet connection and the outlet plugged. Soapy water or other liquid will detect air escaping from between the cups.

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Aavolyn TY655 Fab Cup
[click to enlarge]
Aavolyn TY655 Fab Cup
 

AAVOLYN TY655 FAB CUP DESIGN

AAVOLYN engineers developed the fabricated cup design as the most efficient type of internal coolant design. The Type 655 consists of a fabricated coolant cup composed of a cup and a bushing pressed together to form a sealed internal coolant area. This coolant area has permanent “O” rings on either side to prevent leakage between the pressed joints. The AAVOLYN design brings the coolant areas close to the bore of the case to allow maximum heat transfer. The size of the coolant areas are enlarged to provide a large surface for heat transfer. This design is used in all gas services and all discharge pressures. One of the value added features of the Type 655 is that the “O” ring sealing the coolant flow from cup to cup does not go around the rod. Hence, the rod does not have to be removed to replace them resulting in a major time saver.

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PACKING CUP PURPOSE

Each packing case consists of a series of individual packing cups designed to hold various packing rings. The total assembly acts together to seal the gas pressure from the cylinder. The dimensions of each cup are controlled to ensure the following:

  1. Cup OD consistent with rest of case and fits into the stuffing box with controlled clearance.
  2. The packing groove has side clearance and sufficient clearance on the OD for the packing seal to function efficiently.
  3. The width of the cup allows for enough wall thickness to withstand design pressures of the compressor. The cup width must also allow for features incorporated into it such as the water cooled passages, vent or lube drilling and gasket grooving.
  4. Surface finishes must be consistent with the design pressure and type of gas being sealed.
  5. The bore of the cup has clearance between itself and the piston rod to ensure the case does not come in contact with the rod during operation. The crosshead on one end of the rod and the piston on the other may cause the piston rod to drop during operation.
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 Packing Cup
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Packing Cup
  

GASKET CUP DESIGN

A gasket of various designs is inserted into a groove in the gasket cup or placed between it and the end of the stuffing box to seal the gases from the cylinder. When the gas travels from the higher pressure area of the cylinder along the piston rod, it has two paths that it can take - into the packing case and around the outside of the case into the distance piece. The packing assembly with its various sealing rings is designed to prevent the gas from continuing along the rod. The packing case gasket seals the OD the packing.

Four Case Gasket Designs:

  1. Metal Wire Gasket
  2. Metal Sheet Gasket
  3. Metal Lay On Gasket
  4. Fabric Sheet Gasket

The end packing cup closest to the cylinder is referred to as the “GASKET” cup.

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COOLANT PASSAGE DESIGN

The fab cup featured in the TY655 design consists of an internal packing cup section and an external bushing. A large groove is machined into the internal section to form the cooling passage in the cup. On each side of the cooling passage, “o” ring grooves are located to seal the passage from gas passing through the cup joints. Gas leakage will blow coolant out of the system because the gas pressure is much greater than the pressure used in the coolant system to circulate the cooling liquid.

The number of liquid cooled cups is determined by the gas pressure and the space available for the overall case length.

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Gas Compressor Institute Expo
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Gas Compressor Institute Expo
 

AAVOLYN Corp was once again an exhibitor in the 2010 Gas Compressor Institute Expo held in Liberal, Kansas. Joining the Aavolyn crew this year was Aavolyn distributor, Justin Smith, of Canadian Pipe & Supply located in Moore, Oklahoma.

Pictured from left to right: Justin Smith, Lynn Farrell, John Miguez

  
  

GAS COMPRESSOR INSTITUTE LIBERAL, KANSAS APRIL 2010

With development of the Hugoton Gas Field in the late 1940’s and early 1950’s, many oil and gas companies saw a need for local training of their personnel. It was that need that led organizers to host the first Gas Measurement Institute in Liberal in 1952. About 100 people attended that first event. Encouraged by the success of the first Gas Measurement Institute, the group planned others. That first event has grown into a pair of annual institutes, the largest of which is the Gas Compressor Institute, which attracts more than 1400 people to Liberal each year. For 57 years, the Liberal Gas Institute has provided unique educational opportunities for the petroleum and natural gas industries. The institute features up-to-date and relevant programs designed expressly for field level employees. These presentations deliver both important review material and the latest new information about applicable technologies.

Aavolyn personnel had the opportunity to exhibit at this year’s Institute. Aavolyn’s latest ring designs along with OEM supplied packing assemblies were featured during the exhibit.

Aavolyn is a trusted supplier to numerous Original Equipment Manufacturers worldwide.

Aavolyn products are proudly manufactured by experienced machinists in our Millville, New Jersey location.

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 Gas Compressor Institute Expo2
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Gas Compressor Institute Expo2