Q1. What is an electric actuated slurry valve used for, and where is it used?
A1. A knife gate valve handles media that would jam an ordinary gate valve. It is used on pulp and paper stock, sewage and sludge, ash and mining slurry, and dry powders and granules under hoppers and silos. The blade is a thin knife that cuts through the material as it closes, and the body has a shallow cavity that does not compact solids. It is operated fully open or fully closed rather than throttled, and it is normally expected to give a good shut-off rather than a bubble-tight one, which is why on some duties a small amount of weeping is accepted as normal. On solids lines it is often the only practical isolation valve, and on large slurry lines it is supplied with a flush connection so that the seat area can be washed before the valve is closed. With an electric actuator it is used on lines operated remotely or by a sequence, and on sites where no air supply is available for a pneumatic actuator.
Q2. What design variants are available, and how do I tell them apart?
A2. Knife gate valves come in four practical variants. The wafer body, clamped between two pipe flanges, is the cheapest and is used where the line can be taken out of service easily. The lugged body takes threaded inserts so the valve can be bolted up and the downstream pipe removed while the valve stays in place. The double-flanged body suits lines that must not be disturbed, and the square or rectangular port body is for dry solids and hoppers. The gate itself is either a straight-edged knife for liquid and slurry service or a bevelled / V-notched blade for dry bulk.
Q3. What settings have to be checked when an electric actuator is commissioned?
A3. Four settings decide whether the valve survives. The torque limit — set it to the figure the valve actually needs, because a limit high enough to close a stiff valve is also high enough to damage the seat. The open and close limit switches — verify them at the valve rather than on the actuator alone, since a switch set on actuator travel can leave the valve short of full open or full closed. The stroking time, where a figure is specified, because it protects the line as much as the actuator. And the fail-safe action — test it by removing the supply rather than by reading the drawing. Record all four in the maintenance file; the next person to work on the valve will not know what was agreed at order stage.
Q4. Which standards is this valve designed and tested to?
A4. 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.
Q5. How is the valve pressure tested before delivery?
A5. Every valve is shell-tested and seat-tested before dispatch. The shell test is at 1.5 times the rated pressure at 38 °C with the valve partly open, proving the pressure boundary; the seat test is at 1.1 times with the valve closed, proving the closure. Holding time follows the standard and the size. Acceptance is normally quoted against ISO 5208: Rate A means no visible leakage, while lower rates permit a defined leakage over the test period. The rate that applies should be written into the specification — on gas, toxic or metered service Rate A is the usual requirement.
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.
