3PC Side-Entry Trunnion Mounted Ball Valve Stainless Steel

Overview of the J-VALVES three piece side entry stainless trunnion valve

Side entry is a statement about how the valve is assembled and how it comes apart. The body is in three pieces, and the trim goes in from the side: the end piece comes off, the ball and its seats are withdrawn through the opening, and the valve is rebuilt the same way. It says nothing about how the ball is held in service, which is on the trunnions at the top and the bottom.

The range on this page starts at two inch and runs to fifty six, Class 150 to Class 2500, in 304, 316 or 316L stainless, with a soft or metal seat and flanged or butt weld ends. The photographs on this page are of the eight inch Class 2500 build, which is the size at which the choice between side entry and top entry stops being a matter of preference and starts being a matter of whether the line can be cut.

The argument is that the entry style is a maintenance decision rather than a design flourish. A side entry valve has to have its pipe opened to be serviced. A top entry valve does not. Everything else about the two, the sealing, the trim, the standards they meet, is the same, and a page that sells one over the other on sealing performance is selling a distinction that does not exist.

Design and Construction

The centre piece carries the ball on an upper and a lower trunnion, holds the stem and the gland, and provides the seat pockets. The two end pieces each carry a flange or a weld end and close on the centre on a gasketed joint with its own stud ring, so the valve has two pressure joints and two gaskets at full line pressure.

That construction has an economic logic that is easy to miss. Two identical end pieces mean one pattern, one set of castings or forgings, one machining programme and one inspection routine for both ends. A top entry body is a single large part with a large opening at the top, and it costs more to make before any advantage is realised.

What is bought with the two joints is access from both ends. The centre piece stays in the line, both end pieces come off, and the whole trim including both seats and both trunnion bearings is in front of the fitter. On a large valve that is a real advantage, because the alternative is lifting the entire body out of the pipe.

The trunnions are what hold the ball, and this is where the description of side entry in most catalogues goes wrong. The ball is not fixed to the body by the side entry; it is fixed by the upper and lower trunnion shafts in their bearings, exactly as on any other trunnion mounted valve. Side entry describes the assembly route, and the trunnion describes the support, and the two are independent facts.

The comparison that matters is not about sealing. It is about what has to happen on the day the valve is worked on.

The row that decides most projects is the first one. A side entry valve on a welded line has to have the line cut to be serviced, and that turns a seat change into a hot work permit, a spool piece and a revalidation. A top entry valve on the same line has its bonnet lifted and its trim changed with the body still welded in place.

The second consequence is about weight. On an eight inch Class 2500 body the end piece alone is a lift, and the centre piece with the ball in it is a bigger one. Top entry concentrates the lifting on one item, the bonnet and trim assembly, and leaves the heavy body where it is. On a valve in a confined space that difference in handling is often worth more than the price difference.

Material Options

The stainless body is 304, 316 or 316L, and the choice follows the medium rather than the pressure. The L grade is the low carbon version and sits in a lower material group in ASME B16.34, so it has a lower allowable stress and a lower rating at every temperature, which matters on a high class valve and rarely matters on a low one.

The seat is where the temperature limit and the shut off are set. A reinforced PTFE insert gives tight shut off to about two hundred Celsius, a PEEK insert extends that, and a metal seat goes further at the cost of a leakage rate that is measured rather than assumed zero. On a Class 2500 valve the seat is a heavy ring and the difference in torque between a polymer and a metal face is large enough to change the operator.

The stem, the gland and the trunnion bearings follow. The bearings on a valve this size carry the ball against the full end thrust, and the bearing material decides the operating torque as much as the seat does. A bearing chosen for price will show up as an operator that has to be oversized to compensate, which is a cost that arrives later and is harder to explain.

Technical Specifications

The body joint row is worth writing on the order as a grade in its own right. On a three piece body the end pieces and the centre piece can be supplied in different grades, and a valve with a 316 centre and 304 ends is a valve whose ends will corrode first. The grade of each piece belongs on the order as a separate line, not as one line describing the valve.

Standards and Compliance

API 6D does not prefer one entry style over the other. It sets out requirements for the body, the joints, the stem, the seats and the tests, and a side entry valve and a top entry valve that satisfy those requirements are both conforming articles. A quotation that claims one style is required by the standard is quoting a preference as a rule.

Fire testing is worth a note because a three piece body has two joints that both have to survive the test. The fire test is a type test on a representative valve and its scope covers a range of sizes and classes; a certificate for a small three piece valve does not automatically extend to an eight inch Class 2500 body, and the scope on the certificate is the thing to read.

Manufacturing Process

The three castings or forgings are machined with the joint face, the flange face, the bolt circle and the seat pocket on one centreline, and the two end pieces are machined to the same programme so that they are interchangeable. That interchangeability is the reason a spare end piece can be stocked, and it is also the reason a mismatched pair of end pieces will fit and still not be right.

The seat pockets in the centre piece have to be coaxial with each other and square to the joint faces, because the ball sits in both of them at once. A pair of pockets that are each within diameter tolerance and not coaxial gives a crescent contact band, and a crescent band will pass a bench test and weep at temperature.

Assembly is a sequence that matters: seats and springs, ball, trunnions and bearings, stem and gland, then the two end pieces with their gaskets. The valve is cycled and its torque recorded with the end pieces fitted, because a body that has been machined slightly out of square will show a tight spot that no adjustment at the gearbox will remove.

Quality Control and Testing

The lifting row is specific to a valve this size and this construction. An eight inch Class 2500 three piece body has a centre piece and two end pieces that are each heavy enough to need a proper lift, and the valve should be marked with its mass and with the points that are designed to take it. A valve lifted on its gearbox or on its flange studs is a valve that will be damaged before it is installed.

Applications and Industry Service

Side entry belongs on flanged lines that are opened for maintenance anyway, and in plants where a shutdown is planned and the pipe is broken as part of it. In that setting the side entry valve is the cheaper article and the access from both ends is an advantage rather than a complication.

It also belongs where the valve is small enough that a fitter can handle the end piece by hand, which covers a large part of the catalogue. Below about six inch the handling question disappears and the two joint construction stops being a burden.

It is the wrong valve where the line is welded and cannot be cut, where the valve is buried, and where the valve sits in a position that cannot be reached from both ends. In those settings a top entry body is the correct answer even though it costs more, because the cost of cutting the line once exceeds the price difference on the valve by a wide margin.

Installation, Operation and Maintenance

Plan the access before the valve is installed. Both end pieces have to come away, and on a large valve that means space on both sides, a lifting point above, and a place to put the pieces down. A side entry valve installed against a wall or in a pipe rack with no room on one side is a valve that will be cut out rather than serviced.

Support the body on its own feet or on a saddle and bring the mating flanges up parallel before tensioning. A three piece body that is being pulled into alignment by its pipe flanges will close one joint and open the other, and the open one will weep at test pressure with the gasket taking the blame.

For a seat change the line is isolated, vented and drained, the studs on both end pieces are released in a pattern, and each end piece comes away carrying its own seat. The ball is lifted on its trunnions with the works lifting arrangement, the seat pockets are inspected for erosion, and the trunnion bearings are checked for play. New gaskets go on both joints, the seats are replaced as a pair, and the studs are brought to the drawing figure in a cross pattern in stages.

How to Specify and Order

Six lines fix the valve: size, class, body grade for each piece, seat type, end connection and operator. On this construction there are two more that belong on the order: the entry style, written as side entry or top entry, and the mass and lifting arrangement, which on a large valve is a site instruction rather than a detail.

Three questions belong to the line rather than to the valve: can the pipe be opened, is the valve accessible from both sides, and will it ever be buried or welded in. The first two decide whether side entry is usable, and the third decides whether it is the right choice at all.

Documents to name in the order: the EN 10204 3.1 certificate for each of the three body pieces with its heat number, the positive material identification report, the shell and seat test record with a result per seat and per direction, the torque record with the end pieces fitted, the general arrangement drawing with the face to face dimension, the mass and the lifting points, and the fire test certificate with its scope.

FAQ

Q: What does side entry actually describe?

A: The assembly route. The trim goes in from the side, so the body is in three pieces and one end piece has to come off to reach the ball. It says nothing about how the ball is supported, which is on the upper and lower trunnions in their bearings on every trunnion mounted valve.

Q: Can a side entry valve be serviced without cutting the pipe?

A: Not on a welded line. The end piece has to come off, and on a weld end that means the valve comes out. On a flanged line the joint at that end can be broken and the piece taken off where the valve sits, which is why the entry style and the end type have to be decided together.

Q: When is top entry the better choice?

A: When the line cannot be opened. A top entry body keeps the body in the pipe and the trim comes out through a bonnet at the top, so a welded, buried or inaccessible line can still have its seats changed. It costs more to make, and it saves a line cut, which is usually the larger number.

Q: Why are the two end pieces identical?

A: Because one pattern or one forging die serves both, and one machining programme covers both ends. That economy is the reason the three piece body is cheap to make and the reason a spare end piece can be stocked. It is also the reason a mismatched pair of end pieces will fit and still not be right.

Q: Does API 6D require one entry style?

A: No. API 6D sets requirements for the body, the joints, the stem, the seats and the tests, and a side entry valve and a top entry valve that meet those requirements are both conforming. A quotation that claims one style is required is quoting a preference as a rule.