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How can one sanitary valve handle low-flow dosing and high-flow CIP?
One of the awkward design problems on a sanitary process skid is that the required flow during production can be completely different from the required flow during cleaning. A dosing or blending stage may need very fine control at a relatively low flow rate, while during clean-in-place (CIP), the same line may need a much higher flow to achieve the velocity required to clean the pipework and process components effectively.
Why is this difficult for a conventional control valve?
Control valves are normally sized around a usable operating range. A valve that is large enough to pass the full CIP flow may operate extremely close to its seat during normal dosing, where a small movement can produce a large change in flow. A valve sized for excellent low-flow control may then become a restriction when the system changes to CIP mode.
The conventional answer is often to add a separate CIP bypass path or additional valves. That can work, but it adds components, pipework, control logic, validation points and further areas that must also be cleaned.
Low-flow dosing or blending
The valve provides fine regulation around the required process setpoint.
Higher cleaning flow
Reference pressure is disengaged so the valve can allow full cleaning flow.
Using a wide-range sanitary valve
The Equilibar FD Series sanitary back-pressure regulator takes a different approach. Instead of a conventional globe-style seat, it uses a flexible diaphragm acting across multiple parallel orifices. As the diaphragm moves, a progressively larger or smaller orifice area is exposed.
This creates a very wide usable Cv range and allows the same sanitary valve to operate across markedly different flow conditions. In a suitable application, it can provide fine control during low-flow dosing or blending while opening to accommodate the higher cleaning flow.
The achievable operating range depends on the selected valve size, available differential pressure, fluid properties and control arrangement. Proper application sizing is therefore essential before deciding whether one valve can cover both duties.
What does the control arrangement look like?
For automated flow control, the sanitary FD valve can form part of a closed control loop. A flow transmitter measures the actual process flow, the PLC or process controller compares that value with the required setpoint, and an electro-pneumatic pilot regulator adjusts the reference pressure on the FD valve. The valve responds to the changing pilot signal to maintain the required flow.
This is an inverse control arrangement: increasing pilot pressure moves the diaphragm towards the orifices and reduces flow. The detailed control logic must be designed for the application.
During CIP, the reference pressure must be disengaged to allow full flow through the valve. The available pump capacity, pipework and every other component in the cleaning path must also be capable of delivering the required CIP condition.
Why could this simplify a sanitary skid?
Where the application conditions allow one correctly sized valve to cover both operating modes, the arrangement may offer several practical benefits:
Potentially removes or reduces the need for a dedicated CIP bypass around the control valve.
Reduces the number of valves and pipework components on the skid.
Provides precise control during production while retaining higher maximum-flow capability.
Uses a sanitary, drainable valve design intended for CIP and SIP service.
Supports electronic integration when paired with suitable flow measurement and pilot control.
May simplify cleaning, control logic and validation by reducing the number of process paths.
Where is this useful?
The concept is relevant to pharmaceutical and bioprocess skids where one process path needs to cover both fine dosing or blending and a much higher cleaning duty. Examples include:
- Buffer preparation
- Media addition
- Water-for-injection use points
- Liquid blending
- Filtration support systems
- Other hygienic processes where equipment count and cleanability matter
Do not size the valve on turndown alone
A common mistake is to size around the headline maximum flow without looking closely enough at where the valve will spend most of its operating life. For a dosing skid, the lowest controllable flow can sometimes be the more difficult design condition.
A wide Cv range is useful, but it is not a substitute for proper sizing. The complete operating envelope needs to be considered together:
One valve is not automatically the right answer
A separate CIP bypass may still be appropriate where the required cleaning flow, pressure loss, line size or control conditions cannot be achieved through the selected valve. The aim is to compare both approaches against the real operating envelope, rather than assume that either layout will suit every skid.
Talk to PCT about the operating envelope
If your skid has a large difference between its minimum process flow and maximum CIP flow, send PCT both conditions rather than a single duty point. We can review the required Cv window and whether a wide-range sanitary control arrangement could simplify the design.
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