Change-Over Valves for Industrial Applications | LESER

Change-over Valves for Industrial Applications

  

LESER Best Availability Change-over Valve Type 320

Type 320 Flow

Change-over valve casted

 

type-330-free

 Type 330 Compact
Change-over valve casted

What is a Change-over Valve?

There are two main types of safety valves: Spring-loaded safety valves and pilot-operated safety valves. Also relevant are so-called change-over valves, which ensure continuous system availability.

Change-over valves are switching valves used for the redundant installation of safety valves. Change-over valves switch the flow of media between two different safety valves. The forced control incorporated into the design ensures that one inflow and/or outflow is always open.

Short Explanation

Change-over valves are safety valves that switch the medium flow between two different safety valves, thus ensuring higher plant availability by ensuring that one inlet or outlet is always open.
change-over-valve-design-top
Favourable flow design through incline of seats

Design & Function of Change-over Valves

Change-over valves are used to connect two safety valves with a pipe connection to a pressure system, in order to increase operational availability. One safety valve is in operation and one safety valve is on standby. The standby safety valve can be disassembled and serviced, for example during running operation. The pressure system continues to be protected against impermissible pressure. This way, shutdown periods of the plant can be planned independent of the maintenance cycles of the safety valves.

Change-over valves exist in several designs. These are presented and compared below.

Rotor Design 

In change-over valves with a rotor design, a rotating actuator ensures that one flow path is blocked and the other unblocked. A change-over valve such as this is selected based on the same nominal size as the inlet and/or outlet of the safety valve. But the switching process itself is rather complicated.

With this type of valve and an optimized flow path and low pressure drop, it is possible to do without additional reducers. Only one pressure-drop coefficient is known for each nominal size, however. Effects caused by options or other nominal pressures are not specified. For that reason, there are some uncertainties involved in calculating the pressure drop for these change-over valves.

Shuttle Design

Change-over valves with shuttle design have 2 x 90° deflections. This results in a comparatively high pressure drop. Because of this, they can only be designed in the same nominal sizes as the inlets of the safety valve when the safety valve only has to have a low capacity or the inlet lines in question are relatively short.

For high-capacity safety valves or long piping in the inlet, the shuttle change-over valve must be at least one nominal size larger than the nominal inlet size of the safety valve. This is the only way to achieve the maximum inlet pressure drop of 3%, thereby ensuring the stable functioning of the safety valve.

As with the rotor design, a pressure-drop coefficient is often specified for each nominal size. The effects of reducers or other nominal pressures are not factored in here either. As a result, these valves are subject more uncertainties as rotor changeover valves when calculating the pressure drop.

Pendulum Design

The special design of change-over valves with a pendulum design makes it possible for the active safety valve to be switched reliably during maintenance. The shut-off disc travels along a circular path back and forth between the two outlets. The optimized flow path ensures a minimal pressure drop. Clearly defined flow resistance coefficients in each configuration make it easier to calculate the inlet pressure drop precisely.

The 3% criterion is therefore easy to implement. Designed for maintenance-free longevity and reliable, 24/7 uptime, the new change-over valves have undergone lifecycle tests with 1,000 changeovers with hot, cold and particulate media and at high operating pressure

 

Change-over Valve Types in Comparison

rotor-design-cov

Rotor Design

Inlet Pressure Drop

Optimised flow level



Reliable Uptime (prevent simultaneous closure of both sides)

Complicated change-over in three steps

 

Reliable Uptime (ensure seal tightness)

Sealing problems

 

Coupling on the inlet and outlet sides in lockable combinations

Lockable combination with different nominal sizes of change-over valves on the inlet and outlet of safety valves

shuttle-design-cov

Shuttle Design

Inlet Pressure Drop

Comparatively higher pressure drop due to 2 x 90° deflections (risk of chatter or larger valves required) 


Reliable Uptime (prevent simultaneous closure of both sides)

Easy to operate using a hand wheel

 

Reliable Uptime (ensure seal tightness)

Robust and long service life

 

Coupling on the inlet and outlet sides in lockable combinations

Lockable combination only possible with change-over valves with the same nominal size on the inlet and outlet of safety valves (high weight, reducers) 

pendulum-design-cov

Pendulum Design

 Inlet Pressure Drop

Optimised flow path, pressure drop slightly higher than with the rotor design


Reliable Uptime (prevent simultaneous closure of 
both sides)

Easy to operate using a hand wheel

 

Reliable Uptime (ensure seal tightness)

Robust and long service life

 

Coupling on the inlet and outlet sides in lockable combinations

Lockable combination with different nominal sizes of change-over valves on the inlet and outlet of safety valves 

FAQ

What are Change-Over Valves?

Change-over valves are safety valves that switch the medium flow between two different safety valves, thus ensuring higher plant availability by ensuring that one inlet or outlet is always open.

What is a CoV Valve?

The abbreviation „CoV“ stands for “Change-Over-Valve” and refers to the safety valve type of the same name.

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