Review of Process Pipeline Valves (1)

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Looking into my heating cupboard at home, I see at least four types of valves in use.  The one on the top of my pressurised hot water tank controls the cold water feed from the mains, is a 15mm diameter ball valve with a handy quarter-turn lever.  This is a quick shut-off valve that controls the whole hot water supply.  I also see lots of  in-line ball valves under each basin with screwdriver actuation that act as isolators for each tap – very handy when you are changing tap washers.  The actuated 3-port diverter valve on the boiler outflow pipe is another form of ball valve.

I also see a brass gate valve  on the mains water inlet that tends to stick when you least want it to.  On the radiators I see lock shield valves on each radiator outlet that can be used for fine control.  These are a form of globe valve.  Some of the taps (faucets) on the sink are a form of globe valve which are great for accurate control.   Finally, I see reflux valves on the pump delivery side to stop reverse gravity flow damaging the pump.

I am sure that you are not really interested in my house plumbing per se because they are so familiar to you, but I mention them because the valves represent all the basic types of valve used in the process industry and the wider utility and industrial sectors.  The size, connections, how it is actuated and materials it is constructed from all vary tremendously, but the principle is the same for each ball valve, gate valve, globe valve and reflux (or non-return) valve.

Let us first look at the ubiquitous ball valve.  When I looked at various valve catalogues, I was amazed at the variation of types, standards, duties and constructions.     The straightforward ball valve has a close-fitting stainless steel ball larger than the pipe diameter set with a very short spindle on the top only, that has been bored out such that it is slightly smaller than the pipe diameter.  Actuation can be manual, direct quarter turn or geared) or by geared servo actuation.   Sizes vary from 8 mm to 500 mm diameter and for most pressure duties between 10 and 40bar (150lb to 600lb).

Typical 15 mm dia. ball valve

The variations on this basic type include flow control ball valves where instead of a bored hole, there is a triangular shaped hole with one point perpendicular to the spindle axis.  As the hole opens, only a small area is presented at first and this is progressively increased as the spindle turns through 90 degrees.  For larger sizes and higher pressure duties the humble ball valve turns into a trunnion valve with a spindle (trunnion) right through the ball (and hole) and with two bearings, top and bottom.

For pipelines where pigging is carried out, the hole through the ball is oversize so that the cleaning pig can pass straight through (when the valve is open of course).  Yet another variation is the diverter valve where there are three pipe port fittings and the ball is drilled with a “T” shaped hole.  These valves are for In position one it is closed with the “bar of the “T” against the inlet port; in position 2 at 90 degrees left , flow is diverted to one of the outlet ports and at 90 degrees right, flow is diverted to the other port.  Yet an other form of this type of valve is the butterfly valve where instead of a ball, there is a flat disc that is trunnion mounted.

Next, we go to the globe valve which comes in a variety of forms and sizes from 15 mm to 600 mm and with duties from 10 bar to 100bar.  The valves all feature a two-chamber casting separated by a web that has been drilled and seated to allow a screw actuated spindle mounted plunger to seal this hole.  These unidirectional valves are usually specified for pure liquids and gasses where no leak shut off and fine modulation of flow is required.

The next category is the gate valve type.  These valves are usually available from 15mm to up to 1,000 mm diameter.  They act as a rising and lowering shutter perpendicular to the flow.  These bi-directional valves usually feature a narrow wedge shape that assists in positive seating.  These valves are generally used for clean water or liquid applications.   Conversely, the knife wafer valves in the larger sizes are used to control slurry tank or reservoir outlets or inlets in mining and power station applications.  Seating design is modified to allow self-cleaning sealing surfaces.

Finally we touch on Non-return Valves ( NRV  or reflux valves).  These are used for ensuring that pipe flow remains unidirectional and therefore they are mostly found on pump delivery mains to protect the pump from back flow.   These come in many sizes and types including the lift check valve, swing check valve and spring loaded types.  For high pressure duties above say 2″ (50mm) size, it is usually essential to have these valves anti-slam to avoid the damaging effects of water hammer (hydraulic shock) when the pump stops.

We will be returning to this subject in more detail next time – so keep visiting.

Hasta mañana