PATENTS

12Sealing Technology February 2006

PatentsFree piston with time-varying clearance seal

Applicant: PraxairTechnology Inc, USA

This invention relates generally tofree piston devices, and is particu-larly useful for a piston employedwith a linear motor for providingacoustic energy to a cryocooler. Freepiston devices use reciprocating pis-tons or displacers, but rely on theoverall system dynamics to guaran-tee the proper motion amplitudeand phase of different system com-ponents. As such, there is no natur-al constraint on piston mean posi-tion, which may drift off-centereven if the dynamics are properlyexecuted. In a reciprocating freepiston device with clearance seals,the pistons will tend to drift towardthe side with the greater oscillatingpressure. This is understood to bedue to the higher density of the gasflowing through the seal during thehalf-cycle where the high oscillatingpressure side is high, versus thereverse flow in the other half of thecycle. The invention makes use of

the discovery that hollow pistonscan flex in response to a pressuredifference across the piston shell, sothat in the presence of oscillatingpressure the shell expands duringone half-cycle, thus narrowing theseal gap, and contracts during theother half-cycle, thus increasing theseal gap. In most devices with hol-low pistons, this results in increasedunbalanced mass flux through theseal and increased piston drift. Thisinvention embodies the recogni-tion that a piston can be devisedthat reverses the usual pressure gra-dient on the piston shell, causingthe seal gap to tighten when thepressure is high in front, and viceversa. This essentially makes thepiston seal itself behave like acheck-valve, reducing flow in thedirection that normally causes pis-ton drift/offset.Patent number: WO 2005/089328Inventor: P.S. SpoorPublication date:

29 September 2005

Trocar seal for surgical procedures

Applicant: NeosurgTechnologies Inc, USA

A trocar seal is described that is foruse in laparoscopic surgery, particu-larly to prevent the escape of insulat-ing gas during the performance ofsurgical procedures. The diameter is

expandable from 2 mm to about 13mm. It is preferably fabricated fromsilicone and coated with paralene oranother approved coating.Patent number: WO 2005/094432Inventor: P.T. O’HeeronPublication date: 13 October 2005

Seal for gap between two adjacent components

Applicant: Alstom TechnologyLtd, Switzerland

The invention relates to a seal forsealing a gap between adjacentcomponents, in a turbine or turbocompressor. It is applicable to com-ponents such as guide vanes orrotor blades or a heat shield. Thedesign is intended to maintain an

effective seal during relative move-ment of the sealed components dueto thermal expansion. A number ofdifferent detail designs are includedin the patent.Patent number: WO 2005/095763Inventors: S. Olmes, M. Richter

and T. ZiererPublication date: 13 October 2005

Applicant: Gore EnterpriseHoldings, USA

This patent describes an expandedPTFE tape that is particularlyintended for use on large flangesrequiring a conformable gasketthat will function with low sealingstress. The tape includes a layer

that has low air permeability. Adecrease in leak rate of about 1.5orders of magnitude has beendemonstrated.Patent number: WO 2005/103533Inventor: K.E. DovePublication date:

3 November 2005

Seal removal tool for aircraft air compressors

Applicant: HoneywellInternational Inc, USA

This patent describes a tool that isdesigned for removing the mechan-ical seal from an aircraft air cyclemachine (ACM), the turbocom-pressors used for cabin air supplyetc., without damaging the seal.This can help prevent unwanteddebris being left within themachine. Also, as the seals are gen-erally relatively expensive to replace,if it is undamaged it is preferable forthe seal not to be damaged duringthe removal process, so that it canbe reused when the ACM isreassembled. The seal has a groovedinner surface, and the removal tool

has matching grooves on retractablefingers. To remove the seal the fin-gers of the tool can be expanded tocontact the seal. The method ofoperation and variants of the toolare covered in considerable detail.Patent number: WO 2005/097412Inventors: J.T. Chan, J.M. Hurlbut

and R.S. StoltzPublication date: 20 October 2005

Editor’s comment: This appears to be apotentially useful technique for remov-ing seals from a location with difficultaccess. I am sure, like me, you will bepleased to learn how much the aero-space industry is interested in savingmoney by reusing dismantled seals.

Free piston designed to distort in response to the pressure differentialand maintain the correct pressure balance, from WO 2005/089328.

Example of the seal removal tool disclosed in WO 2005/097412, showingthe grooved fingers that are expanded to mate with the seal.

Coil gasket utilizing expanded PTFE tape