This report contains a degree project made by the mechanical engineering students Lennart Andersson and Daniel Jansson. The project has performed in assignment by SOMAS Valves AB in Säffle. SOMAS are leading in development on control and on/off valves. To maintain this position they always want to improve their products. One way in this development is valves that are more tightened.

The purpose with our project was to investigate another seat design on a HiCo (High Cobalt Alloy) seat to a SKV 150 PN 25 valve and compare this to an original HiCo seat.

By modifying the seat on a ball valve we want to achieve a valve that leaks lesser then a valve whit original seat. At the same time the maneuver torque should be retained or better and the wear should not be worse.

The project begins with a theoretic investigation of valve forces, maneuver torque and seat design. A manufacturing drawing was made in Pro ENGINEER and handed over to SOMAS AB for manufacturing. Four seats are made in the new design and will be compared with four original seats about maneuver torque, tightened and wear. The idea to make a trace in the middle of the seat was that it would tighten earlier.

Water under pressure is pressed against the valve to test its resistance of leaking, the leaking is measured by a measure glass. The modified seats leaks more then the original seats, even though, according to the theory they should have a higher seat force. Even the maneuver torque is higher on the modified seats, but this increase is not a problem. All seats was tested to watch their resistant to wear, to test this, a valve mounted with seats is opened and closed 600 times (about 3hours). Because of the short wear time it’s hard to see and validated wear, but on the after coming pressure test the valve is more tightened.

A reason to leaking is the tolerances between the seats and the ball. The reason why the modified valve seat leaks more is probably that the lathe area functions as a channel for the medium.

The medium which passes the first tightened area can easier find a new way to pass the second tightened area.

The conclusion is that the new seat design is nothing to go further with, but there are proposals for a new seat design.