Keofitt W9 - 3.9 Pressure and vacuum

KEOFITT W9 USER MANUAL V.4 PAGE 15
3.8 Parts and Accessories
Keott provide a huge number of spare parts and accessories to the entire range of sampling valves.
These include accessories like:
• Barbed ttings and tube welding ttings for tubes and hoses
• Adaptors between Tri-clamp, Mini Tri-clamp and Hose Piece (Quick Coupling)
• Spike Bag holders and Spikes
• Fitted PTFE tubing for Quick Coupling and Tri-clamp
• Any length of PTFE tube
• Proximity sensors
• Clamps for Tri-clamp connections
• Hypodermic needles
• Click-on steamer
• Circulator
• Aseptic Sampling Bags
• Sampling bottle systems
and spare parts like:
• O-rings and gaskets
• Chains and bushings
• Handles and Tommy Bars
• Set screws
• Membranes
3.9 Pressure and vacuum
Pressure ratings:
All valves with the exception of valves with valve head type B features a spring to provide the closing
force against the valve seat. The spring is dimensioned such that all valves must pass a pressure test up
to 10 bar. At some tank pressure above 10 bar the spring will give way and the valve will leak.
A nominal max. constant pressure of 6 bar allow suicient tolerance to cater for the most common
pressure peaks in a process line.
In the type B valve head the closing pressure is exerted by turning the knob rmly by hand; it closes like
an ordinary water tap. In this way, this valve may be used in equipment with a nominal max. pressure of
12 bar.
Vacuum ratings:
On installations where vacuum may occur temporarily, rubber membranes (EPDM, FFKM, Silicone) are at
risk of being sucked hard into the valve seat, whereby the valve might not open properly. However, the
additional (closing) force from the vacuum (corresponding to max. -1 bar(g) or 0 bar(abs)) is rather small
(10%) compared the force exerted by the spring (corresponding to at least 10 bar(g)), so there is no risk of
damaging the membrane as long as the vacuum is only present when the valve is closed.
Besides, attempting to open a sampling valve under vacuum makes no sense, since nothing will ow out,
so the incident is rather improbable.
Rubber membranes will seal perfectly well against vacuum, when the valve is kept closed.
WARNING: When opening the valve while the process side is under vaccum there is a risk that the
membrane may be sucked past the valve seat and into the valve opening, which could cause the
membrane to be damaged.
On installations where vacuum will occur, PTFE membranes don’t have the risk of being sucked into the
valve seat, but as it is a harder and less exible material a complete tightness against the ambient air
may not be secured.