DN50x40 PN20 A105 Two Piece Extended Stem Floating Ball Valve

Overview of the J-VALVES DN50x40 PN20 A105 Two Piece Extended Stem Floating Ball Valve

Two flange standards are printed on this valve and one of them has no PN 20 in it. Class 150 is written PN 20 in the pressure code of API 6D, and that is where the number comes from. EN 1092-1, the European flange standard, steps from PN 16 to PN 25 and has nothing in between, so a valve described as PN 20 with EN flanges is describing a joint that cannot be cut. The two flanges are also not interchangeable at this size, because their bolt circles and outside diameters differ even where the class is nominally the same.

That is the first thing to settle before the valve is quoted, and it is the reason this page leads with the joint rather than with the body. The second thing is the stem: an extended stem is a site dimension dressed as a product option, and the length is decided by the insulation or the burial depth rather than by the valve. Both are settled on the drawing before a price is meaningful.

Design and Construction

The body is two pieces: a main body and one end cap on a bolted joint that carries the gasket. The trim enters through that joint, so a seat change is a flange off and a cap off rather than a valve out of the line. At DN50 that is a bench job for one person, which is the honest argument for the design at this size, and it is also why the joint gasket is worth stocking as a spare.

The bore is reduced: the ends are DN50 and the passage through the ball is DN40. The valve is therefore dimensioned as a two inch valve and flows as a one and a half inch one, which matters when the line has been sized on the pipe rather than on the valve. It is a deliberate economy, not a manufacturing shortcut, and it is visible on the drawing as a step behind each seat.

The ball floats between two seats, so the line pressure pushes it downstream and the sealing force rises with the pressure. At this bore and this class the load is small enough that the seat and the stem carry it without trunnions, which keeps the body compact and the torque low enough for a lever. The stem is a separate shaft from the ball with its own seal, and the anti blowout shoulder is on the stem rather than on the gland.

Material Options

The body is A105, a forged carbon steel, supplied normalized and used for water, oil, gas and steam within the carbon steel range. It is the ordinary choice for a line that is not corrosive, and at this size the forging is small enough that the heat number on the plate can be traced to a single certificate. The alternative grades on the original page are a low temperature forging and a stainless one, and both are quoted against the order rather than stocked.

The ball is carbon steel with a hard chrome deposit, or a 304 or 316 stainless where the medium would attack a carbon face. The deposit is what the seat runs against, so the finish is a service item: a scratched chrome ball will wear a soft seat faster than a correct one, and on a buried valve the inspection that would catch it happens once, before the trench is closed.

The seat is PTFE, with reinforced PTFE and PPL as the alternatives, and the packing is graphite or PTFE. The extended stem does not change any of that: the extension is a shaft, and the seal that matters stays at the body. What the extension does change is access, because the gland can be reached from grade rather than from inside a pit. That is why the packing grade is chosen for the temperature at the body and not for the temperature at the handle.

Technical Specifications

The class is Class 150 and the pressure code is PN 20, and those two statements describe one rating. What they do not describe is the flange. At this size there are two joints in common use: Class 150 to ASME B16.5, and PN 16 to EN 1092-1, which is the European step nearest to it. A PN 25 flange is also offered where the line is rated that way, and it is a different joint again. The order has to say which one, and the drawing has to show it.

The ends are raised face on either standard. Face to face follows the table for the flange that is ordered and the figure for the build is dimensioned on the signed drawing, because a valve cut to one flange standard is not automatically the same length as one cut to the other. The operator is a lever with a locking hole, with a gear, a pneumatic actuator or an electric actuator available where the valve is under a cover or out of reach.

The stem length is not a catalogue dimension. It is set by the insulation thickness plus the clearance needed for the lever, or by the depth from grade to the pipe centre on a buried line, and it is quoted against those two figures together with the drawing. Weight follows the length, so it is quoted rather than tabulated, and so is the height of the grade box where one is supplied. Two lines on a drawing settle it; a range in a catalogue does not.

Standards and Compliance

ASME B16.34 gives the rating and the minimum wall, and API 608 gives the general ball valve requirements: marking, pressure test and the fire safe option. Where the line is a pipeline, API 6D applies instead and asks for more, including cavity relief and a documentation package. On this valve the class is low enough that the structural requirements are not the difficulty; the joint is.

The pressure code is the part that gets confused. API 6D pairs Class 150 with PN 20, and that pairing is a code, not a flange. EN 1092-1 lists its own PN steps and PN 16 is the one that sits nearest to Class 150 at this size, with PN 25 above it. So a valve that is correctly described as Class 150 / PN 20 can be fitted with either PN 16 or PN 25 flanges, and the buyer has to say which. Writing PN 20 and leaving the flange standard off is how a valve arrives with a bolt circle that does not match the counter flange.

API 598 sets the shell test at one and a half times the rating and the seat test at one and one tenth times, and the acceptance on a soft seat is no visible leakage. The test is run on the body before the extension is fitted, which is worth knowing when a witness is invited: there is no point waiting to see a test that has already happened. Where a fire safe design is required, the order names API 607, API 6FA or ISO 10497, because a certificate to one is not evidence for another.

Manufacturing Process

The body and the end cap are forged, normalized and then machined from the flange faces. The flange is faced and drilled to the standard that was ordered, the bore is machined through with the step for the reduced port, and the joint face is finished before the seat pocket is cut from it. Because the same casting or forging can be drilled to two different flange standards, the drilling is the last operation on the flange and it is the one that decides which valve this is.

The extended stem is assembled after the body is built and tested. The stem is joined to an extension shaft through a coupling that carries the torque but not the pressure, and the extension passes through a guide or a protection tube that keeps it straight when the trench is backfilled. The alignment of that shaft is the part that decides whether the lever turns freely ten years later, so it is set with the body on a bench rather than in the trench.

Quality Control and Testing

The forging certificate is written against the heat number stamped on the body, and the ball and stem certificates follow the same pattern. Where the order asks for a positive material identification report, that report is issued against the same heat; it is quoted on request rather than claimed as a standing practice. The flange drilling is checked against the standard ordered rather than against the valve next to it on the bench, because the two may be for different lines.

The shell test runs at one and a half times the Class 150 rating with the body assembled, and the joint and the gland are watched along with the wall. The seat test follows in both directions at one and one tenth times with the cavity open, and the acceptance is no visible leakage. After testing the valve is stroked, the extension is turned by hand to check for binding, and the plate is read against the certificate before the ends are capped.

Applications and Industry Service

This valve is bought for buried lines, for insulated lines and for lines where the operator has to stand at grade: district heating and cooling, tank farm transfer, water mains with a buried section, and plant piping under a jacket where a lever at the valve body would be inside the cladding. In those services the stem length is part of the installation drawing rather than part of the valve description.

It is the wrong valve where the flow needs a full two inch bore, where the line is pigged, and where the medium would attack a carbon body. It is also the wrong valve where the joint has to be broken often, because a buried valve is a valve that is installed once, and a seat change on it means digging rather than opening a body.

Installation, Operation and Maintenance

The valve is set so that the extension is vertical and the operator clears the insulation or the grade box, with the protection tube fixed to the body rather than to the pipe, so that pipe movement does not bend the shaft. The flanges are brought parallel before the studs are torqued, and the joint is made to the table for the standard that was ordered, because the two standards do not share a torque value.

On a buried line the valve is not packed with grease and left; the extension guide is the part that needs attention, and it is reachable from grade. The gland can be adjusted from the top without exposing the body, which is the practical benefit of the extended stem and the reason it is specified at all. A seat change is a trench and a body joint, which is why the seat material is chosen for the life of the line rather than for the cheapest quotation.

How to Specify and Order

The order needs size, class, flange standard, body material, bore, seat, stem length and its reference points, operator and test standard. Write the flange standard explicitly: ASME B16.5 Class 150, or EN 1092-1 PN 16, or EN 1092-1 PN 25. PN 20 alone is a code and not a flange, and leaving it alone on the order is how a valve is made to the wrong joint.

Write the stem length with its reference points as well, because a length with no reference is a number that two people will measure differently: from the body centre to the top of the extension, against the insulation thickness plus clearance, or against the depth from grade to the pipe centre. A drawing with those two lines on it is worth more than a longer description, and it is the document the works will build to.

FAQ

Q: Is PN 20 the same as PN 16?

A: No. PN 20 is a pressure code that API 6D pairs with Class 150, and it is not a flange step in EN 1092-1, whose steps run through 16 and then 25. A Class 150 valve can be fitted with either a PN 16 or a PN 25 flange, and the two joints differ in outside diameter and bolt circle at this size. The class describes the rating; the flange standard describes the joint.

Q: Which flange should the order say?

A: The one the counter flange on the pipe is cut to. On an ASME line write ASME B16.5 Class 150. On a European line write EN 1092-1 and then choose PN 16 or PN 25 to suit the line rating, because there is no PN 20 to write. If the line is mixed, the flange nearest the valve decides, and the rest of the joint is made up with an adapter rather than by asking the valve to be both.

Q: Why is the stem extended, and who decides the length?

A: The stem is extended so that the operator and the gland sit outside the insulation or above grade, rather than inside the cladding or in a pit. The length is a site dimension: insulation thickness plus clearance on an insulated line, or the depth from grade to the pipe centre on a buried one. It should be written on the drawing with its reference points, because the same number measured from two places gives two different valves.

Q: Does the extended stem move the seal?

A: No. The packing and the gland stay at the body, and the extension is a shaft that carries torque only. The stem seal is still the part that holds the pressure, which is why the extension does not change the pressure rating and why the gland is adjusted at the body end. What the extension changes is where a person stands, and whether the gland can be reached without opening the insulation.

Q: What does the reduced bore cost?

A: It costs flow area and it buys a smaller ball, a lower torque and a lighter valve for the same pressure boundary. On a DN50 line with a DN40 bore the pressure drop across an open valve is small but not zero, and a line sized on the pipe rather than on the valve will notice it at high velocity. It also rules the valve out of any pigging duty.

Q: Can this valve be used on a buried line?

A: Yes, and that is what the extended stem is for, but the installation has to protect the shaft. The extension is guided or run inside a protection tube fixed to the body, the trench is backfilled so that the pipe does not settle against the shaft, and the operator is set in a grade box that drains. A buried valve with an unguided extension is a valve that will not turn after the first winter.