Q1. What is a metal seated ball valve used for, and where is it used?
A1. A ball valve isolates or switches flow with a quarter turn of a bored ball. It is used wherever the valve is operated often or has to be operated quickly and visibly: on-off duty on water, oil, gas and chemicals, at the inlet and outlet of instruments and small pumps, on manifold and sampling points, on filling and emptying connections, and on gas lines where a tight seal matters. Compared with a gate valve the advantages are speed, a seal made by a seat that wipes itself as the ball turns, and no cavity in line with the flow. The limits come from the seat material: the polymer seats that give bubble-tight shut-off set a temperature ceiling, and the bore through the ball adds a small pressure loss that a full-bore design is used to avoid.
Q2. What should I watch during installation, operation and maintenance?
A2. Ball valves are quarter-turn devices and are meant to be worked fully open or fully closed; using one to throttle erodes the seat and, on a soft seat, heats it until it deforms. Leave the valve in the position it will spend its life in, and operate it periodically so the seat does not take a permanent set. On buried or extended-stem valves grease the stem bearings through the fittings provided, and on gas service check the cavity relief path. When the valve is opened after a long shutdown, open it slowly, because the pressure that has built up in the cavity releases suddenly.
Q3. Which standards is this valve designed and tested to?
A3. Where a customer specifies a different standard — DIN, EN, GB or a client specification — it can be worked to, but it should be named at enquiry stage, because it changes dimensions, the material list and the test acceptance at the same time. Two details are worth settling early because they are easy to leave to assumption: the revision of the standard that applies, and which edition of the pressure–temperature tables is being used for the rating.
Q4. How is the valve pressure tested before delivery?
A4. Two practical points are worth fixing before the order is placed: whether the seat test is carried out in both directions or only in the specified flow direction, and whether a test certificate with the recorded figures is required or a simple pass statement will do. On isolation valves for gas and hazardous media the recorded figures are normally asked for and filed with the maintenance record, because they are the baseline against which later leakage is judged.
Q5. How does it compare with the alternative valve types on the same line?
A5. The alternatives worth comparing are the ones that could do the same job at a different cost. A butterfly valve is lighter and cheaper as size grows and needs little space, but its disc sits in the flow and its seat is more easily damaged. A gate valve costs more at small sizes but holds tight more easily and gives an unobstructed bore when open. A ball valve gives quarter-turn operation and is better where the valve is cycled often. A globe valve is chosen only when some regulation is wanted, because it costs permanent pressure drop. A check valve is not an alternative to any of them — it prevents reverse flow and cannot isolate.
Q6. How do I select the right one for my line?
A6. Selection starts from the service, not from the catalogue. Fix the medium and its concentration first, because that decides the body material and the seating. Then the design pressure and the design temperature together, since the allowable pressure at temperature is lower than the cold rating and it is the hot figure that governs. Then the size, the connection, and how often the valve will be operated, which is what decides between a handwheel, a gearbox and an actuator. Bring those five answers to the enquiry and the rest of the selection follows from them.
Q7. How do I order, and what information is needed for a quotation?
A7. Send the line size, pressure class, medium, working temperature and required connection. Add anything the line demands — sour service, low temperature, a pigging requirement, a control-room signal — and the quotation will come back with the material and seat selection confirmed rather than assumed. Non-standard sizes, alternative operators, trim material and coating can all be produced to order.
