1. Start With Your Pipe Size — But Don’t Stop There
Knife gate valves are usually installed full-line size, meaning DN100 pipe → DN100 valve.
However, this is only a starting point, because:
Slurries behave differently from clean liquids.
Flow may need to be controlled, not just shut off.
Undersized or oversized valves can cause clogging or wear.
Rule of thumb:Match valve size to pipe size unless special conditions require otherwise.
2. Understand Your Medium (This Is Critical)
Knife gate valves excel in difficult media, so the type of medium directly affects sizing.
Ask these questions:
Is the medium clean, fibrous, abrasive, or thick?
Does it contain solids, and if so, how much (%)?
What is the particle size?
Why it matters:
Thick or solid-heavy media may require larger bore sizes to reduce blockage.
Very abrasive fluids may require seal types and coatings rather than a size change.
Fibrous media may need full-port designs to ensure proper cutting and closure.
✔ If your medium tends to settle or clog easily, consider full-bore or oversize options.
3. Check Flow Requirements (Cv / Kv Values)
To ensure proper flow capacity, review the valve’s Cv (US) or Kv (EU) rating.
Higher Cv/Kv = more flow at a given pressure drop.
Consider:
Required minimum and maximum flow rate
Acceptable pressure drop across the valve
Whether the valve will be used only for isolation or also for throttling
Knife gate valves are primarily shutoff valves, not designed for precise throttling, but sizing must still support required flow.
✔ If flow restrictions are a concern, verify that your selected size provides enough capacity.
4. Look at Operating Pressure and System Design
Knife gate valves—especially lug and wafer types—have pressure limitations.
When sizing, ensure:
The valve size matches the system’s pressure class (PN10, PN16, ANSI 150, etc.)
Larger valves do not exceed allowable pressure ratings
The system does not create excessive pressure drop when the valve is open
✔ Larger valves can sometimes mean lower pressure ratings, so cross-check performance charts.
5. Evaluate Installation Constraints
Sizing is not only about fluid — it’s also about where the valve will be installed.
Consider:
Face-to-face dimension availability
Space for actuator mounting
Whether manual, pneumatic, or electric actuators will be used
Vertical vs. horizontal pipe orientation
Maintenance clearance
✔ Ensure the physical size fits the real-world installation.
6. Consider Knife Gate Valve Type
Uni-directional valve
Designed for flow in one direction
Higher sealing efficiency
Usually same size as pipeline
Bi-directional valve
Handles flow from both sides
Needed for slurry pipelines
May require slightly larger sizing due to seat configuration
Full port vs. reduced port
Full port → best for slurries and solids
Reduced port → may reduce cost but increases clogging risk
✔ For slurries, always choose full-port, uni- or bi-directional based on flow direction.