Metal working – Method of mechanical manufacture – Process for making bearing or component thereof
Patent
1998-08-07
2000-06-20
Cuda, Irene
Metal working
Method of mechanical manufacture
Process for making bearing or component thereof
2989808, B23P 1500
Patent
active
060762594
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a method for the replacement of valve bearings, and more particularly to the replacement of a trunnion bearing on a rotary valve.
In a typical modern Francis turbine-type hydroelectric power station, each of the turbines can be provided with a rotary main inlet valve (MIV) which isolates the turbine from the high pressure penstock during normal operation and for maintenance purposes. Normally the MIV operates in a balanced condition, that is to say, at zero flow. The MIV is closed whenever its associated turbine is either shutdown or is spinning in air. The MIV is similar to a conventional ball valve except that there is a clearance between the moving rotor and the valve body. This clearance is closed at each end by steel rings which slide axially in the body under hydraulic control.
The ring at the downstream end is called the service seal and operates automatically as part of the normal operating sequence of the turbine. The ring at the upstream end is called the maintenance seal and usually remains open, only being closed for isolation purposes. Each MIV is rigidly connected to an associated upper high pressure penstock on the upstream side. On the downstream side, the MIV is connected to the turbine via a dismantling joint. The dismantling joint acts as a sliding coupling to absorb axial movement of the MIV during operation and, when removed, gives access to the service seal assembly and turbine casing, and also permits removal of the valve body end cover.
the normal procedure for replacement of the MIV trunnion bearing necessitates the de-watering of the reservoir and the penstocks. This usually requires a complete station shutdown with a considerable loss of generating income and the additional risk of possible local damage to the high pressure concrete lined penstock when the internal pressure is removed.
In modern power stations, particularly those housing pump-turbines, the number of cycles of load experienced by the trunnion bearings of the MIVs far exceeds that of the trunnion bearings of the MIVs far exceeds that of older conventional power plants. This has greatly increased the need to avoid a complete station shutdown in order to replace the trunnion bearings.
Hitherto, however, there has been available no method of replacing the trunnion bearings of an MIV whilst retaining the pressure in the high pressure penstock, because, when the balancing pressure on the downstream side of the valve is removed, the load on the trunnion exerted by the pressure of water in the high pressure penstock makes it impossible to remove the trunnion bearings. Typically the load on the closed valve rotor can be up to 3,500 tonnes and, in order to remove the trunnion bearing, it may be necessary to support and hold the valve rotor to a positional tolerance of plus or minus 0.1 mm to enable the trunnion to be centralised in its diametral bearing clearance.
According to the present invention, there is provided a method for removal or replacement of a rotary valve trunnion bearing which comprises transferring the load from the trunnion bearings to an axially adjustable support means controlled by a pressurisable closure means and retained by a mechanical locking means.
According to one aspect of the invention there is provided a method of removing or replacing a trunnion bearing of a rotary valve connected to a high pressure penstock which comprises: rotor on its downstream side; downstream side of the support means; pressure-retaining closure means to balance the load due to the pressure at the upstream side acting on the valve rotor; valve rotor against the upstream load and to bring the rotor and its trunnions in a location enabling its bearing to be removed; mechanical locking means; pressure-retaining closure means; trunnion is substantially centrally positioned in its bearing; and
Preferably the support means comprises a support ring, which is preferably adapted to move axially, for example, in response to hydraulic pressure between the support ring and the pressure-retaining closure me
REFERENCES:
patent: 3134336 (1964-05-01), Huffman et al.
patent: 4262691 (1981-04-01), Kacal
patent: 5295300 (1994-03-01), Garrick, Jr.
Moss William Owen
Stockton Roy
Cuda Irene
First Hydro Company
Kvaerner Boving Limited
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