How to Choose Between Normally Open & Normally Closed Angle Seat Valves
Introduction
When selecting a pneumatic angle seat valve for your packaging machine, one of the most common questions is:
Normally Open (NO) or Normally Closed (NC)?
The wrong choice can lead to:
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product waste
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unsafe machine behavior
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unnecessary air consumption
At Kinko, we help packaging OEMs and end users make the right valve selection. This guide explains how to choose between NO and NC angle seat valves with practical rules and a comparison table.
1. Quick Definition
| Valve Type | State without air pressure | State with air pressure applied |
|---|---|---|
| Normally Closed (NC) | Closed (no flow) | Open (flow) |
| Normally Open (NO) | Open (flow) | Closed (no flow) |
Both types use spring return to default position.
The difference is whether the spring holds the valve closed (NC) or open (NO).
2. How to Choose – Simple Decision Rules
Ask yourself these three questions:
Question 1: What should happen when air / power fails?
| If failure must → | Choose |
|---|---|
| Stop flow (safe shutdown) | NC |
| Keep flow (process drainage / cooling) | NO |
Question 2: What is the normal operating state?
| Normal state | Choose |
|---|---|
| Valve is closed most of the time | NC (energize only to open) |
| Valve is open most of the time | NO (energize only to close) |
Question 3: Air consumption matters?
| Situation | Better choice |
|---|---|
| Want to save compressed air | Choose the type that stays in its normal state most of the time |
| Long cycle life requirement | Either works — Kinko valves are rated for ≥2M cycles |
3. Typical Applications for Each Type
| Application | Recommended Type | Reason |
|---|---|---|
| Liquid filling nozzle | NC | No dripping when idle; air opens to fill |
| Tank drainage | NO | Valve opens on air failure to drain safely |
| CIP return line | NC | Closed when system stops |
| Cooling water bypass | NO | Cooling continues even if air fails |
| Foam / detergent dosing | NC | Precise on/off control, closed at rest |
| Emergency vent line | NO | Opens on failure to relieve pressure |
4. Comparison Table: NO vs NC Angle Seat Valves
| Feature | Normally Closed (NC) | Normally Open (NO) |
|---|---|---|
| Default state (no air) | Closed | Open |
| Air required to change state | Yes (to open) | Yes (to close) |
| Most common in packaging | ✅ Yes (~80% of cases) | ❌ Less common |
| Suitable for fail‑safe close | ✅ Yes | ❌ No |
| Suitable for fail‑safe open | ❌ No | ✅ Yes |
| Air consumption when idle | Zero | Zero (no air applied) |
| Typical application | Filling, dosing, metering | Drain, vent, cooling bypass |
5. Technical Parameters (Kinko NO/NC Angle Seat Valves)
Both NO and NC versions share the same mechanical specifications.
| Parameter | Value |
|---|---|
| Valve size | DN10 – DN65 (3/8″ to 2‑1/2″) |
| Body material | SS304, SS316L |
| Seal material | PTFE (standard), FKM, EPDM, NBR |
| Operating pressure | 0 – 16 bar |
| Control air pressure | 4 – 8 bar |
| Max. medium temperature | -10°C to +180°C (PTFE) |
| Cycle life | ≥ 2 million cycles |
| Actuator type | Single acting, spring return |
Kinko advantage: Both NO and NC are available from stock in common sizes.
6. Common Mistakes to Avoid
| Mistake | Consequence | Correct action |
|---|---|---|
| Using NC for continuous open application | Valve energized 24/7 → coil heat, shorter life | Use NO instead |
| Using NO for fill nozzle | Product drips when air fails → waste | Use NC instead |
| Ignoring fail‑safe requirement | Unsafe machine state during power outage | Define fail‑safe first |
| Assuming all brands offer both types | Delayed delivery | Choose Kinko — both types available |
7. Quick Selection Flowchart (Text Version)
Start: What happens on air failure? → Must CLOSE (safe) → Choose NC → Must OPEN (drain/vent) → Choose NO If no failure preference: → Valve closed most of time → NC → Valve open most of time → NO
8. Summary – One Sentence Rule
Use NC for filling and dosing (fail‑safe close).
Use NO for drainage and venting (fail‑safe open).
For standard packaging machine applications, NC is the safe default choice — but always check your fail‑safe requirement first.
9. Need Help Choosing？Kinko Can Help
Kinko offers both Normally Closed and Normally Open angle seat valves in:
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SS304 / SS316L
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BSPP, BSPT, NPT threads
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Multiple seal options
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OEM marking available
Contact Kinko for sizing recommendations and sample testing.
Ivan (Mobile:+86-18968769287)
WhatsApp：+86-13579991606
Wechat:+86-18968769287
Website：www.kinko-flow.com
ZHEJIANG KINKO FLUID EQUIPMENT CO.,LTD