Above image shows a diagonal valve arrangement for HIPPS (high integrity pipeline protection system) application
During his career in the oil industry, Derek Thomas designed a full-bore diagonal valve that could provide high integrity pipeline protection. He later produced a working model that clearly demonstrated the valve’s practicality. Mr Thomas would be delighted if an established manufacturer could take these designs and start to produce diagonal valves.
By David Sear
One of the more unusual stands at the 2002 Valve World Exhibition featured a fully-working, full-bore diagonal transparent valve model which had quite literally been put together in a garage!
The valve’s inventor, Mr Thomas of PETSA Consulting, was keen to see if an established valve manufacturer might take his concept from the design stage to full-scale production. Despite plenty of interest, there were, however, no takers.
The working model (see YouTube for a video of the model in action) was therefore returned to the garage and Mr Thomas’ time was again fully absorbed by his growing consultancy work.
But now, in retirement, Mr Thomas believes that the valve community might be more interested in a totally sealed valve and actuator system, especially given the heightened attention to fugitive emissions of greenhouse gases such as methane.
Such a valve would also be ideal for HIPPS use with no need for external instrumentation.
As shown in Figure 1, the valve body (A) is simply two bores, intersecting at an acute angle, typically between 25 and 45 degrees.
Flow (green) passes along the smaller bore. There is only one moving part: the grey piston (B) moving within the larger bore. A diagonal hole (C in Figure 2) through the piston lines up with the smaller bore (D) through the body when the valve is open. This requires a mechanism to prevent rotation of the piston: splines, a pin in a groove or slot, or other such device.
Figure 2 shows the valve in its closed position. The seals (E and G) between the piston and the larger bore also seal the smaller bore, preventing flow along it. This is the fundamental principle of the valve.
The outer seals (F) only move within the larger bore, maintaining fluid containment and also pressure balance, so that the piston stays where it is left, with a low force requirement to move it.
This principle provides a full-bore flow path, which would allow the passage of a pig. It permits the use of several standard or nonstandard seal elements of various types.
One such arrangement might comprise a metallic, initial seal (piston ring, G), to resist erosion, with one or more elastomeric or plastic final seals (O ring, quad ring, chevron seal stack, lip seal, etc, E).
The space for additional seal elements increases with a larger difference in bore widths and a more acute angle of intersection between them.
The fundamental principle could be applied in a valve which is mechanically operated by means of handles (valve stems) screwing inwards or outwards to move the piston.
All the above-described advantages would apply, and the outer piston seals would provide an additional safeguard to prevent leakage at the stem seal packings of the operating screws.
Mr Thomas would be delighted if an established manufacturer could take these designs and start to produce diagonal valves.
This is illustrated in Figures 3 and 4, respectively in open and closed position. Integral, hydraulic actuation is achieved by simply adding sealed end plugs (H and I) and fluid inlet and outlet ports (J and K) to the larger bore.
Pumping a power fluid into the space between an end cap and the piston and venting the equivalent space at the other end of the piston will move the piston.
In Figures 3 and 4 the anti-rotation mechanism for the piston (B) is illustrated by a pin (L) through the piston, moving within a slot (M) in a rod extending from the end cap (H); many other mechanisms are possible.
This embodiment is compact: it eliminates a separate valve actuator and has only one moving part. It eliminates stem seal leaks (fugitive, environmentally harmful emissions) as the end caps can be permanently sealed, without movement, and the actuator fluid system can be completely sealed and use an innocuous power fluid.
Such a sealed power fluid system would need a high-pressure rating and/or a relief system, in case of a leaking outer seal on the main piston, although its normal operating pressure might be much lower than that of the controlled flow, as the piston is pressure- balanced.
Operation could be purely mechanical-hydraulic (e.g. hand pump and manual valves or relief valves), electrical (pumps and relief valves) or electro-hydraulic (pumps and solenoid valves).
Switches could be included to indicate the end of piston travel (full operation).
This application is principally intended for use at pressure specification changes: oilfield wellheads, lines or separators, or processing plants of many types. It protects against downstream blockages or inadvertent shut-ins.
It is simple, reliable and purely mechanical, eliminating the need for separate sensors and actuators, being self-contained with integral sensor and actuator. It only vents innocuous power fluid (normally, back into the power fluid system).
For this important application only changes to external pipework are needed to the design illustrated in Figures 3 and 4, although they might also be incorporated into the design of the valve itself.
Upstream pressure provides closing force, by means of a connection (N) between the upstream inlet to the valve (or a point upstream of the valve itself) and the space between an end cap and the piston at which higher pressure provides closing force.
If the controlled flow is of a dirty or dangerous fluid, it might be desirable to include either a filter or a floating, isolation piston within this connection, illustrated by a box (Q) in Figure 5.
The space between the other end cap and the piston leads past a “tee” to a relief valve (or even two in parallel, for additional reliability), illustrated by a box (O) in Figure 5, which determines the isolation pressure.
When line pressure exceeds the relief valve rating, power fluid vents through the relief valve (probably back into the power fluid system), as the piston is driven to the “closed” position by the increasing upstream pressure.
To open the valve again, power fluid is pumped back, into the “tee” connection, through the vent/re-open line, until the piston reaches the end of its travel to the “open” position.
If separate vent and re-open lines were to be used, such re-opening would only be only possible once upstream pressure has been decreased below the relief valve rating, and power fluid would vent through the relief valve when the piston reaches the end of its travel to the “open” position.
By incorporating a check valve (P) into this line, as shown, a single line (W) may be used to vent fluid upon actuation of the valve and to re-set it to the open position afterwards (regardless of upstream line pressure, so caution must be exercised, or the re-opening pressure positively limited to less than that of the relief valve rating).
Mr Thomas was not aware of any industrial application of this principle and submitted a patent application in 2003. That failed, mainly due to a 1972 US patent (3,682,200) concerning a position valve. It is likely that previous patents have lapsed, but potential manufacturers should check this and be aware that they cannot claim proprietorship of the basic principle. Nor can Mr Thomas, of course, but he would derive considerable satisfaction at seeing this design put into effect.
Working model of the diagonal valve with key components and operation highlighted
• Water inlet is from a garden hose (1), at left.
• Between that inlet and the Perspex valve body (9) a tee (2) takes off water for actuation, at line pressure.
• The white and red devices (3, 4, 5, 6, 7) are washing machine solenoid valves, powered by mains electricity via the orange cable (8), each with a separate switch.
• Within the valve body (9) the brass piston (10) is in the closed position.
• It is prevented from rotation by a pin which goes through a slot in the rod which is part of the lower end cap.
• In “open” position the switch with the printed label (10) opens the upper left, white valve (3) and the bottom right, red valve (6) to allow flow (with left, blue-handled valve (11) fully open, and right one (12) partly open to maintain some operating pressure). Water is dumped from the red valve at bottom right.
• In “close” position, the same switch (10) opens the lower left, white valve (7) and the top right, red valve (4), with water dumped at top right.
• With the main valve (9) in open position, with just the white solenoid valve at bottom left (7), and the white solenoid valve at middle right (5) open, closure of the blue handled valve at right (12) would cause pressure to rise and water is then vented through the red-capped relief valve (13) at right, and this causes the main valve to close (HIPPS operation).
• In either open or closed positions of the main valve (9) both white solenoid valves (3, 7) at left can be closed, and both red ones (4, 6) at right opened, to demonstrate that the main brass piston is pressure balanced and stays where it is.
Meet Derek Thomas
Derek Thomas spent his entire career in the oil industry. His first position was with Schlumberger, which he joined after graduating in Physics from St. Catherine’s College, Oxford University, in 1966. After working as a field engineer in Latin America and the North Sea, he progressed to their headquarters technical staff, field-testing and introducing new equipment for well-bore measurement world-wide.
From 1977 he worked for BP, firstly in the North Sea as a petrophysicist, but with widening field technical responsibility leading to a Petroleum Engineering Manager position in Indonesia. After a period as Production Manager for BP’s Middle East and Africa interests he spent his final ten years with BP managing upstream R&D projects and their up-take in the field. These covered much of the petroleum engineering spectrum and included work on sealing technology and valves.
Upon retiring from BP in 1999, Mr. Thomas started PETSA, a petroleum engineering consultancy, mainly working on the provision of appropriate technology to resolve well and reservoir performance problems.
Mr Thomas can be reached on: email@example.com
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