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The BFM® fitting works and seals perfectly in almost all negative pressure applications.  

Our fittings are often used in applications where they are operating in vacuum situations, typically where the plants are drying or processing dry powdered-type products and need the equipment to be under a slight negative pressure to avoid leaking dust out of machinery.

It is important when specifying a connector for use in negative pressure situations that the amount of movement, environment, temperature and nature of the pressure are all taken into account.

Connector Length

As a general rule on vacuum, the maximum length of the BFM® blue band connector should be no longer than its diameter without support rings. For instance a 100mm (4") diameter BFM® connector should be no more than 100mm (4") long. This is because the vacuum will pull the connector walls inwards, which will eventually close the connector. 

See the tables below for maximum negative pressure recommendations.

BFM® Connectors with Support Rings

Stainless Steel Support (SS) rings (top left) can be used to negate the effects of length.

For instance, a 400mm (16") long connector will hold as much vacuum as a 100mm (4") long connector if it has three support rings (100mm (4") apart).

The rings also help keep the connector walls open and away from the product flow (see adjacent photo).

Plastic support rings (shown left) can also be used for metal detection applications.

BFM® TR (Tool Release) Connectors

BFM® manufactures a range of connectors where the cuff has a stronger seal in the spigot, and requires a tool to release the connector. The cuff on the TR connectors is far more difficult to release and this can provide an element of added security.

Although the BFM® connector will not release from the spigot when using a TR connector, the connector itself will be under a lot of stress, and the connector walls will be hardened and sucked inwards.

If you have a connector 200mm (8") long or greater, SS Rings should be considered (see tables below)

BFM® Flexi Connectors

The BFM® flexi has a stainless steel spiral wire wrapped in Urethane and are commonly used on two applications:
1.  Light vacuum applications.
2. Where it is critical that the connector is held open while it moves up or down and as the product flows through the connector.

BFM® flexi connectors are available in diameters between 100mm - 300mm (4 - 12") in 50mm (2") increments.  The 'Flexi' range includes standard FlexiFlexi-Light and Flexi-Earthed options.

Large Diameter BFM® Connectors

For diameters over 650mm (26") that will encounter vacuum, it is strongly recommended that you talk with a BFM® representative

The BFM® fitting will handle vacuum at gauge pressure of up to -1000mm w.g on short length connectors, although this will depend on the application and the environment.

Maximum Recommended Operational Pressures

The following chart shows the maximum recommended operational working negative pressure for BFM® Seeflex 040E connector by length for standard and TR (tool release) versions, both with and without stainless steel support rings.  

Connectors with rings set at the recommended 100mm (4") spacing negates the effect of connector length.  TR connectors can also operate at a higher negative pressure than standard connectors. 


Stronger Vacuums

The BFM® fitting has been tested up to absolute vacuum on a number of connectors. All the connectors tested held vacuums far in excess of the limits we have provided, however we would not recommend using any urethane connector over the set limits as this will be a strain on the whole system and the connector will not function at their peak levels. 


NOTE: The BFM® connectors were tested in a static test rig under ambient temperatures. The SS Rings on the connectors tested were set at 100mm centres. Although the suggested limits are well within our tested results, the conditions in which the BFM® fitting will be installed must be taken into account. Please contact BFM® if you have any doubts. Always test on site first.

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