FAQ-I008
Why does the system use a flow control valve?

Q:  Why does the IS-IBC1® use a flow control valve instead of using only a variable speed blower?

A:  Variable speed drives are an important part of good IBC control.  The key is how the variable speed drives are used.  With the significant enhancements in variable speed drive technology, it is not uncommon to question, "Why not just eliminate the flow control valve and use a variable speed blower?"  The reason variable speed blowers should not be used for bubble size control has nothing to do with the variable speed drive or the blower, and everything to do with the volume of the ducting between the blower and the blown film die.  The farther away the blower is from the die, the longer it takes to change the size of the bubble.   The delay is caused by the time it takes to first change the pressure in the ducting. The bubble size will change only after the ducting has changed pressure.  Using this type of control scheme on small bubbles or bubbles with low melt strength materials will result in poor layflat control.

The flow control valve eliminates nearly all of the delay caused by the volume of the ducting.  This is done by mounting the valve near the die (generally within 4-10 feet).  The blowers operate normally and provide a reservoir of pressure behind the valve.  The flow control valve then meters the precise amount of air into the bubble and provides a much faster response than can be provided with only a variable speed controlled blower. 

Date of Last Update: 06/01/2005

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