What is a dual-butterfly non-return valve?

Dual-butterfly non-return valves are butterfly valves, which describes their structure very well. In the middle, there is a closing shaft with two symmetrically hemispherical closing plates on either side.

The dual-butterfly non-return valve’s undeniable advantage is its low flow resistance, which depending on the flow is only a few millibars. In other models, it can be a hundred times higher. The valve’s flow resistance can also be adjusted by selecting different springs. The flow resistance depends on the valve’s installation orientation and the springs used. For example, in a vertical pipe when the flow is from bottom to top, the force required to open the valve is greater than, for instance, in a horizontal pipe.

Selecting a dual-butterfly non-return valve

Unlike its competitors, GESTRA uses two separate shafts and each closing plate is secured by two individual closing springs, whereas normally closing springs are not used at all. The robust design is intended to prevent the valve from being damaged by minor hydraulic water shocks. If the system’s water shocks are significant, BB dual-butterfly non-return valves can be equipped with separate hydraulic dampers.

BB dual-butterfly non-return valves are available in various materials.

Our sales representatives can provide you with more detailed information on the opening characteristics of each valve and assist with sizing if needed. They will help you select a dual-butterfly non-return valve that meets the requirements of your application.

What is a butterfly non-return valve?

Of the non-return valves installed between the discs, the models equipped with a butterfly disc are the simplest in operation. The closing disc is pivoted on one side and the valve is installed with the pivot facing upward. Gravity keeps the disc in the closed position, but it opens when the flow coming from the correct direction reaches the valve. Reverse flow does not open the check valve.

Selection of a butterfly non-return valve

We assist in the selection and sizing of a check valve that meets the requirements of the application.

The butterfly non-return valve is a typical check valve for water systems. The seating retention of GESTRA CB butterfly non-return valves has been reinforced with a separate closing spring, making them extremely robust. In larger sizes than DN 100, the flow resistance is clearly lower than with the GESTRA RK model. However, if low flow resistance is a procurement criterion, the flow resistance in the butterfly non-return valve remains significantly higher than in the double-disc check valve.

Damped Water Hammers

Backflowing liquid can cause a high closing force/pressure that the valve components cannot withstand. It is quite typical that from sizes DN 500 upward, a closing damping is used. Damping can also be used in smaller sizes.

Damping can be done hydraulically, where damping pistons directly slow the disc movement. Another method is using a gear (mechanical/hydraulic). In this case, the disc’s lever is connected to the lever of a hydraulic cylinder. Both have a gear that dampens the closing force.

With gear-equipped damping, a higher duration of closing pressure can be achieved than with purely hydraulically damped valves. It is important to determine the closing pressure in a failure situation. For example, when the pump stops, the pressure of the back-flowing water should be determined before sending out a request for quotation. Damped check valves are typically of the tilting disc (tilting disc check valve) or double-disc type.