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Robust design

Stop valves and control valves for difficult media
Robust design

When conventional valves reach their limitations as operating conditions become more severe, ball sector valves come into their own. As a result, they are particularly suitable for all aggressive and abrasive media in the chemical, pharmaceutical, ore and cement industries, the water and effluent industries, paper and cellulose industries, power, heat and gas production.

Dr. Rainer Lange

The key element in a Ramén ball sector valve is a hemispherical shell – the ball sector. One part of the hemispherical shell provides the shut-off action while the other part has an aperture with a diameter which is normally 80 % of the nominal size of the valve. During opening and closing, the ball sector is turned through 90°. As this happens, the shape of the aperture’s cross section changes from completely circular in the open position to elliptical as it is closed. This design device reduces the risk of the valve becoming clogged when it is opened a small amount, or wearing out at higher flow rates, or draining water from solids in suspension. Even under the most severe operating conditions, in these cases the ball sector is able to seal the medium by means of an easily replaceable seat ring against the body.
Normally, ball sector valves are fitted such that the medium flows against the spherical surface of the ball from the upstream side. The narrowest cross section of the flow is therefore at the valve inlet and the maximum flow speed occurs inside the valve body. If abrasive media have to be controlled, it is advisable to reverse the installation. The narrowest flow cross section, and thus the greatest flow speed then occur at the valve outlet, that is, outside the valve body. The flow rate in the valve body is very low thus reducing wear.
Excellent control curve
The ball sector shape of the control element produces a characteristic curve which can be shown as a modified equal percentage line. This characteristic shape represents an optimum for most operating conditions, particularly when the differential pressure acting on the valve falls as the aperture angle increases. The effective operating curve changes, as this happens, to an increasingly steeper gradient and tends towards a linear curve which, from a control standpoint, is ideal. Furthermore, this characteristic shape is relatively tolerant to over-dimensioning since, even when only partially using the Kvs, the valve covers an ample control path/-angle. Added to this is a good rangeability of about 100:1.
Design details
The large-sized bearing stems for the ball sector eliminate maintenance, while its PTFE composite bearing shells in the valve body ensure that it turns smoothly. The frictional forces and, therefore, a significant proportion of the torque required to actuate these valves are very low. The special shape of the valve body ensures that the differential pressure on the valve has very little effect on the actuating torque. Therefore, for any given nominal valve size, the actuating force is constant regardless of the differential pressure.
The seat ring is made either from graphite-filled PTFE or stainless steel, depending on the application. The sealing face of the stainless steel seal ring is plated. An elastic O-ring made from a variety of elastomeric materials determined by the process – PTFE, EPDM, Viton or Kalrez – forces the seal ring against the surface of the ball sector, thus providing a seal in both directions of flow. The seal ring is attached at the circumference by a retaining ring and by the ball sector when the valve is open, as well as being protected from the effects of the flow. This design makes exchanging the seat ring very simple during maintenance work without having to dismantle the valve.
For operation at high temperatures, the seat ring can be manufactured in stainless steel and be seated against the surface of the ball sector using spring washers and a PTFE seal. The bearing seal is then installed using gland packing material.
Broad range of applications
Ramén ball sector valves can be obtained in DN sizes 25 to 300 for PN 10 to PN 40 depending on the nominal size with Kvs values from 0.25 to 3840. They are made in W 1.4408 stainless steel as well as in special materials such as titanium or hastelloy. Depending on the seal material used, the ball sector valves can be used up to 200 °C.
cpp 400

Schubert & Salzer
VDMA
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