Check Valve

 1 — Overview

A check valve in electric water heaters is installed on the cold water inlet to:

• Prevent backflow

• Balance pressure

• Provide limited pressure relief

👉 In water heaters, it is more than a simple non-return valve

2 — Check Valve vs Non-Return Valve

Feature Non-Return Valve Heater Check Valve

One-way flow ✔ ✔

Reverse flow allowed ❌ ✔ (limited)

Pressure balancing ❌ ✔

Thermal expansion relief ❌ ✔

👉 Conclusion:
All check valves are non-return valves, but heater check valves are more advanced

 3 — Why Water Heaters MUST Have a Check Valve

Without it:

• Hot water can flow back into cold line

• Pressure inside tank becomes unstable

• Thermal expansion has no control path
  
  

👉 Result:

• Tank stress

• Enamel damage

• Leakage risk

✔ That’s why it is mandatory in heater design

 4 — Types of Heater Check Valves

1 — Standard Check Valve

• Basic one-way + pressure balancing
  
  

2 — Check Valve with Manual Relief Handle

• Has a small lever / hand control

• Used to:

  • Relieve pressure manually

  • Empty the tank

👉 Very useful for maintenance

Note : Some norms check valve with handle is mandatory like Saudi Arabia ( SASO ).. 

 5 — Working Principle

✔ Normal Operation

• Water flows from supply → tank

• Valve opens normally
  
  

⚠️ Reverse / Expansion Condition

• Water heats → expands

• Tank pressure increases

• Valve allows slight reverse flow

 6 — Pressure Behavior (Very Important Section)

Pressure Difference Control

• Valve reacts when:
  👉 ΔP ≈ 1 bar (0.1 MPa)

Meaning:

• Tank pressure > supply pressure by ~1 bar

• Valve starts balancing

Maximum Pressure Relief (Dripping Mode)

When pressure reaches valve rating:

👉 Typical valve set pressure:
6 – 10 bar (usually ~8 bar)

What happens:

• Valve releases small water drops ( can connect small hose from the valve to the home dran )

• Pressure is reduced

• Tank pressure stays near valve setting

✔ This is micro-relief (dripping), not full discharge

 7 — Manual Relief / Drain Function

In valves with handle:

• You can open valve manually

• Functions:

  • Drain tank

  • Release pressure before maintenance

👉 Important for:

• Service engineers

• Safe disassembly
  
  

8 — Technical Specifications

Parameter Typical Value

Thread BSP G1/2 or G3/4

Material Brass / Stainless Steel

Working Pressure 6 – 10 bar

Typical Set Pressure ~ 9 bar

Temperature Up to 95°C

Functions Check + Balance + Relief

 9 — Installation Notes

• • Install on cold inlet only

  • Follow flow direction

  • Do not block outlet

  • Use PTFE tape

  • Ensure drain path if dripping occurs

10 — FAQ

Is this valve enough for safety?

👉 No — it provides limited relief only

Why does the valve drip water?

👉 Because pressure reached ~9 bar and it is relieving pressure

What is ΔP = 1 bar?

👉 Difference between tank pressure and supply pressure that triggers balancing

Can I use it to empty the tank?

👉 Yes — if it has a manual handle

👉 Available in the engineering resourses 2D&3D dowinlods

🔗 Related Engineering Resources

Heating Power Calculation  

Heating Element Power Calculator  

Heating Time Calculator  

Electric Water Heater Tank Design  

Tank Volume For Family Calculation  

Tank Volume Selection For Family Calculator  

Surface Loading in Heating Elements  

Flange and Thread Standards (BSP / Metric)