Triple offset butterfly valve torque 1

[bao2ye]

I have a question on the triple offset butterfly valve torque and hope the experts here can help.

Question:

why the ETC torque is lower than BTO torque for triple offset butterfly valve products?

Many thanks

 

[PeterIgg]

Generally the valve is installed with the flow tending to keep the valve closed - one of the offsets being the the shaft is not centrally located through the vane, therefore there is a larger area against which the pressure acts to 'close' the valve than open it. Hence when one comes to open the valve this force has to be overcome. When closing the valve the line pressure assists the action.

 

[bcd]

What PeterIgg mentions, plus also the difference between static and dynamic friction. When closing, the sealing surfaces are moving so it has lower friction. When opening, the sealing surfaces are static (not moving), and is why it is called "break" to open.

 

[bao2ye]

Many thanks to Peter and BCD.

 

[BryceBunting]

Triple Offset Valves or TOVs have an Elliptical Shaped Seat. When TOV Manufacturers tout "Dynamic Torque Sealing" they are highlighting the Sealing Mechanism (Torque Seated) and the reason the torque at Seating is so high, since the Elliptical Seat is being compressed into a circular shape. This is why a Torque Seated valve can be in the proper position, but still not seal unless the correct torque is achieved.

The BTO or Break to Open torque is actually lower regardless of line pressure and hydrodynamic torque. Hence if there is was no pressure on the valve, the ETC or End to Close Torque will still be higher.

Let me know if you have any questions!

 

[TOVmania]

What BryceBunting commented make me wonder what kind of torque seating mechanism quad offset design utilizes.