Dry Gas Seal Boosters
GCS Dry Gas Seal Boosters are available in a variety of boost pressures and flow rates.
What design standards are used?
The boosters have no welded joints. The materials used in fabrication of the wetted parts of the booster conform to NACE MR0175/ISO 15156-1.
Design calculations and allowable stresses from the ASME Section VIII, Div. 1 Boiler and Pressure Vessel Code were used to design the booster but the booster is not code stamped. Under clause U-1c(2)c a code stamp is not required.
The boosters conform to CE ATEX . II 2 G c T3
Boosters with pressure ratings of 200 bar or less do not requir PED.
Boosters with pressure ratings in excess of 200 bar are certified to conform with PED.
What materials are used?
The standard models are machined from 316L SS for the wetted parts and anodized aluminum for the air drive components. 316L SS air drive components are available. The wetted parts can be fabricated from other corrosion resistant materials such as 22% chrome duplex, super duplex, Inconel 625 etc.
We offer a wide range of static elastomeric seals to meet various corrosion, pressure and temperature requirements. Dynamic seals are carbon-fiber-filled Teflon®.
Is it possible for oil to get into the process gas?
No. The booster is non-lubricated on both the gas side and the drive air side. All of the dynamic seals are filled Teflon®.
What drive air quality is required?
Instrument air with a -40°C pressure dewpoint and particulates filtered to at least 5μ. The ISO air classification is ISO 8573.1 Class 2.2.2 .
Can other drive gases be used?
Nitrogen can be used if it meets the air quality standards. If the booster is in a closed space, the nitrogen from the exhaust muffler will have to be piped to a safe location so as not to displace oxygen in an environment inhabited by personnel.
Process gas can be used if it meets the air quality standards. Process gas from the exhaust muffler port and the air pilot valve breather ports must be piped to a safe place or a flare.
Is a drive air lubricator required?
No. The booster is designed to run on dry, non-lubricated air. If the drive air has a pressure dewpoint much higher than -40°C, it is possible that ice will form inside the control valve and cause the booster to stop cycling. Air line lubricators suppress the formation of ice in the valve and may permit operation with drive air that does not meet the required dewpoint specification. Lubricated air will not damage the booster.
How is leakage handled from the rod seal on the process gas side of the booster?
The booster has a distance piece between the drive air cylinder and the process gas cylinder. There is a rod seal cartridge on the process gas end of the distance piece. Process gas leakage past this seal travels into a cavity in the distance piece where a vent port is provided to enable the gas to be piped to a safe place or a flare.
What is the maximum pressure rating for the rod seal vent cavity?
The rod seal vent cavity is designed to collect rod seal gas leakage which can be piped to a flare. It has a maximum allowable pressure of 25 barg which is well above flare pressures but much lower than the process gas cylinder.
Is it possible for the drive air and the process gas to mix?
No. The booster has a distance piece between the drive air cylinder and the process gas cylinder. There is a two-sided drive air rod seal cartridge on the drive air end of the distance piece. One seal faces the drive air cylinder. The other seal faces the distance piece vent cavity. Between these two seal faces is an atmospheric vent port with a breather. Drive air which leaks past the rod seal flows out of this breather. Leaked gas in the distance piece vent cavity is at very low pressure and is contained by the seal which faces the vent cavity.
What is the operating life of a booster?
Boosters are designed for 2500 hours (about 10 million cycles) of service life before a rebuild is required. They can operate 24 hours a day, seven days a week at cycle rates as high as 100 cpm.
Is there a way to tell when maintenance is required?
We offer an optional 1/4 NPT port on the air cap of the booster. An electronic pressure switch can be attached to this port. Every cycle of the booster would trigger this switch. The number of cycles can be accumulated on a PLC and a rebuild can be performed at 10 million cycles.
The item which wears first in the booster is the high pressure rod seal in the distance piece on the process gas side of the booster. Rod seal leakage is usually 0.03 to 0.1 slpm. Leakage in excess of 1 slpm would indicate a need to rebuild the booster
What happens if the high pressure rod seal catastrophically fails?
We have no knowledge of any catastrophic process gas rod seal failure. The seal design is a spring-loaded filled-Teflon® cup seal. This seal is part of a cartridge which includes a filled-Teflon® bushing. The gap between the rod and the distance piece in which it is mounted is 0.4 mm maximum. The bushing and cup seal (32 mm OD by 14 mm thick) would have to extrude through this gap to fail catastrophically.
What are typical booster failure modes other than wear?
The most common cause of booster failure is particulate matter which jams the 4-way air control valve on the drive air cylinder. This valve has a lapped stainless steel sleeve and a honed stainless steel bore. It has a very close fit between the spool and sleeve (less than 0.01 mm). A very small particle can jam this valve and cause the booster to stop cycling. The advantage of this valve is that it has no wear parts and will last for tens of millions of cycles. The recommended air quality must be maintained to protect this valve.
Another cause of booster failure is drive air which does not meet the -40°C dewpoint requirement. When the booster cycles rapidly, the drive air cylinder sees more than 100 air expansion cycles per minute. The expanded air is cold and travels through the four-way control valve. The valve assembly gets very cold and ice from moisture in the drive air starts to form inside the valve which will cause it to seize. This causes the booster to stop cycling. Ice from ambient air humidity will form on the outsides of the booster but it does not prevent the booster from operating.
Another cause of booster failure is a jammed check valve. The booster has two inlet and two discharge check valves which are connected to the process gas cylinder. These are poppet style check valves. The clearance between the poppet and sleeve is about 0.2 mm maximum. Inadequate filtration can cause a poppet to jam in the sleeve from particulate contamination. The booster will cycle but fail to build pressure.