Sealing rings smooth valve operation
A
James Walker and Co product story
Edited by the Engineeringtalk editorial team
Nov 13, 2003
Supagraf LF low-friction sealing rings significantly reduce the torque needed for efficient valve operation - effectively cutting power consumption and allowing smaller actuators to be used.
Supagraf LF low-friction sealing rings are designed to reduce significantly the torque needed for efficient valve operation - effectively cutting power consumption and allowing smaller actuators to be used.
They also have the potential to cut shaft seal friction on pumps that use graphite rings.
The new rings are particularly effective on valves that handle dry gases and other process media where the friction on standard graphite seals is unacceptably high, leading to valve stem sticking and hesitation.
Independent tests confirm the low-friction claims.
When fitted in a gland housing at 10 and 40MPa compressive stress, Supagraf LF displayed friction coefficients of 0.11 and 0.07, respectively.
The coefficients for standard graphite rings were exactly double at 0.22 and 0.14.
Torque-versus-cycle results proved even more impressive.
In extended tests, valve stem torque remained constant at 5Nm for Supagraf LF, whereas for standard graphite rings the torque rose from 21 to 25Nm during the first 300 operating cycles.
With a lubricated valve stem, the torque for standard graphite rings increased from 7 to 23Nm during the first 150 cycles as the lubricant was removed by valve action.
The secret of success for Supagraf LF is a special coating, 5um thick, sinter-bonded to the surfaces of the expanded graphite rings before the moulding process.
With this coating the rings have performed 20,000 low-friction valve stem cycles with fugitive emission control of methane gas to 50ppm or less.
Further tests showed satisfactory performance up to 60,000 cycles with normal manual adjustments along the way.
The new rings will operate at temperatures from -200 to +350C, or at a maximum system pressure in valves of 150bar.
They are chemically inert to media in the range pH 0-14, and also have a fire-safe capability.
Supagraf LF moulded rings are supplied in endless form or, for ease of installation, with a single split and as matched scarf-split halves.
Inside diameters range from 2 to more than 1100mm: sections from 1.5 to 40mm.
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Contact James Walker and Co
Tel +44 1270 536000
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