3"600LB WCB Two Piece Floating Ball Valve

Overview of the J-VALVES 3 Inch 600LB WCB Two Piece Floating Ball Valve

A floating ball has no trunnions, so nothing holds it in the middle of the body. Line pressure pushes it downstream into the seat on that side, and the contact between ball and seat is what seals. That is elegant, it needs no extra parts, and it works for as long as the pressure keeps pushing the same way. It also means the seal is not a mechanical arrangement at all, it is a balance of forces that a change in pressure can undo.

At three inch and Class 600 that balance is worth thinking about, because this is about the last size where the valve is operated by hand and the pressure is high enough for the forces to be large. A pump stopping, a branch reversing, or a column of liquid stopping too fast will all reverse or unload the pressure across the ball for a moment. In that moment the ball can leave its seat, and what it does next is the subject of this page.

Design and Construction

Two pieces with one bolted joint, and the joint sits between the ball and the pipe on one side, which is why the trim comes out that way. The ball has clearance to move along the axis between the two seats, and that clearance is what makes the design work: pressure pushes the ball until it touches one seat, and the upstream seat is then not in contact at all. Only one seat seals at a time, in the direction the pressure is pushing.

That is also the weakness. The movement that lets the ball find its seat is the same movement that lets it leave, and the distance it can travel is the clearance between the seats. A ball that is pushed off its seat and returns travels that distance and arrives with whatever energy the pressure difference gave it, and the thing it arrives against is a polymer seat ring inside a two piece body.

Material Options

The body code is WCB, a cast carbon steel, which is the normal body for a three inch Class 600 valve and needs no argument. The seat is PTFE as standard with reinforced PTFE or PPL listed for temperature, and a metal seat on request. On a valve that sees pressure reversals, the seat material matters more than usual, because a seat that has taken a compression set from an impact is a seat that no longer seals in the direction that matters.

The ball and the stem follow the body code unless the order says otherwise. Where the medium is corrosive the body code changes and the whole valve is ordered against it, and where the service is cold enough for a low temperature steel the code changes to a forging suited to that. Neither change affects the mechanism described here, which is a property of the floating design rather than of the alloy.

Technical Specifications

Three numbers are settled before anything else is discussed: the size, the class and the bore. The flange is an ASME B16.5 Class 600 raised face pattern in three inch, the bore through the ball is full, and the face to face is taken from ASME B16.10 for a flanged valve of this size and class. The built length is on the signed drawing rather than here. Class 600 is PN 100 in the API 6D code. None of those three numbers says anything about what happens when the flow reverses, which is the subject of this page and the reason a floating ball behaves differently from a trunnion one.

The number that matters for this page is not on the data sheet at all: it is the closing time. A hand lever closes this valve over a second or two, which is slow enough that the pressure wave has somewhere to go. An actuator that closes it in a fraction of a second is a different hydraulic event entirely, and the valve that was fine on a lever is not automatically fine on a fast actuator.

Standards and Compliance

ASME B16.34 supplies the wall and the rating; API 608 is the quarter turn product standard that governs a three inch Class 600 floating valve, with API 598 for the shell and seat acceptance figures. None of the three says anything about what happens when the pressure reverses, because a valve standard describes a valve in a steady state rather than a valve in a transient.

That gap is why the transient belongs in the system design rather than in the valve specification. Water hammer is a piping phenomenon: it comes from a column of liquid being stopped, and the valve is only the thing that stopped it. The answer is usually a change in the system, such as a slower closure, a bypass, or a different valve position, rather than a different valve.

Manufacturing Process

The body is cast, inspected and machined, with the joint face and the seat pockets cut from one datum so that the two seats are coaxial. That coaxiality is what the floating ball relies on: the ball finds whichever seat the pressure pushes it against, and if the two pockets are not in line the ball has to tilt to reach the second one, which puts an edge load on the ring instead of a face load.

Assembly is the ball and the upstream seat into the body, the downstream seat into the end cap, and the cap closed over a new gasket with the studs brought down in a cross pattern. The valve is then cycled, which beds the ball against both seats in turn, and only after that is it tested. A valve tested before cycling reads high on torque and can read well on leakage, which is the wrong combination.

Quality Control and Testing

The shell test is at one and a half times the rating and the seat test at one and one tenth times, in both directions, with the cavity open. On a floating ball the two directions test two different seats, and a valve that passes one and weeps on the other has a pocket that is out of line rather than a damaged ring. Both directions are recorded rather than summarised.

The test cannot reproduce a surge, and no standard asks it to. What the test can do is establish that both seats seal statically, which is the baseline the transient is measured against. On a valve that is going onto a line with a known surge problem, the useful additional record is the operating torque after cycling, because a seat that has been impacted reads higher the next time the valve is closed.

Applications and Industry Service

This valve is for three inch lines at Class 600 where the duty is isolation: process branches, utility headers, and the isolation points around equipment. It is operated by hand, it stays at one end of its travel, and in that service the floating design is entirely adequate and cheaper than a trunnion valve of the same size, with fewer parts to wear and a lighter lever.

It becomes the wrong choice in three situations. On a pump discharge where the pump stops without a check valve, the reversal is regular rather than exceptional and a trunnion valve removes the mechanism. On a line where the valve is closed by a fast actuator, the closure itself generates the transient. And on a line with a long column of liquid and a high velocity, the surge energy is large enough that the seat is not the part to be relying on.

Installation, Operation and Maintenance

The valve position matters. Installed with the seat that seals in the direction of normal flow on the downstream side, the ball sits against that seat while the line is running, and the return travel after a reversal is short. Installed the other way round it still seals, because a floating ball seals both ways, but the ball has further to travel each time the pressure changes sides, and the impact is correspondingly larger.

Where the line has a surge problem, the fix is upstream of the valve: close it slowly, leave a bypass open until the flow has stopped, or fit a check valve so the column is stopped somewhere other than at the ball. When a valve on such a line is opened for maintenance, the seat rings are inspected as a pair and the ball is checked for a flat where it has been hammering, because a flattened ball will hold a rate and lose it again.

How to Specify and Order

The order line needs size, class, body style, body code, bore, seat material, end facing, operator and test standard. Where the valve will be actuated, the closing time belongs on the order as well, because it is the difference between a valve that closes and a valve that generates a pressure wave. That item is almost never written and almost always matters on a line that has had a surge event.

The documents to read before acceptance are the plate, the certificate and the drawing. The plate carries size, class, code and heat number; the certificate says what that heat was; the drawing carries the face to face, the flange pattern and the joint torque. On a valve that is going to see pressure reversals, the drawing is also where the seat material should be recorded, because that is the part the transient will damage first.

FAQ

Q: How does a floating ball seal if nothing holds it in place?

A: Line pressure holds it. The ball sits between two seats with clearance to move along the axis, and pressure pushes it into the seat on the downstream side, so the contact between ball and ring is what seals. That means only one seat is in contact at a time, and the seal exists only while the pressure keeps pushing in the same direction.

Q: What happens when the pressure reverses?

A: The ball lifts off the seat it was resting on and travels across the clearance to the other seat, which is the seat on the other side. It arrives with the energy the pressure difference gave it, and it lands on a polymer ring inside a two piece body. Repeated reversals work the ring and can mark the ball, which is why a valve on a line with regular reversals is better served by a trunnion design.

Q: Is a hand lever better than an actuator for this valve?

A: Not better in general, but safer on a line with a surge risk, because a hand closes the valve over a second or two and gives the pressure wave somewhere to go. An actuator that closes in a fraction of a second is a different hydraulic event, and if it is chosen the closing time belongs on the order along with the valve.

Q: Which way round should the valve be installed?

A: Either way seals, because a floating ball seals in both directions, but the travel after a reversal is shorter if the ball is already resting against the seat that faces the normal flow direction. On a line with a known surge problem, that orientation reduces the distance the ball has to travel and therefore the impact when it gets there.

Q: How do I fix a water hammer problem?

A: In the system, not in the valve. Close the valve more slowly, keep a bypass open until the flow has stopped, or fit a check valve so the column of liquid is stopped somewhere other than at the ball. Changing to a trunnion valve removes the floating mechanism from the equation but does not remove the pressure wave, which will find the next weakest thing in the line.

Q: Does the shell test prove the valve will survive a surge?

A: No. The shell test is a static proof at one and a half times the rating, and a surge is a transient that can exceed the static pressure for a moment and then reverse. What the test establishes is that both seats seal statically, which is the baseline. Surviving the transient is a matter of the system and of how the valve is operated.