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Clamping Mechanisms

Introduction

In order to resist internal pressure or external pressure and root intrusion, couplings have to exert suitable contact pressure between the pipe wall and the rubber seal.  In order to ensure that couplings still function effectively throughout their design life, the initial contact pressure has to account for the natural stress relaxation that takes place in the elastomer. Flexseal products use elastomers that meet the requirements of BS EN 681:1 and as such the amount of stress relaxation that takes place over the design life is a known quantity. The initial contact pressure therefore has to be large enough to allow this stress relaxation to occur and still maintain a seal at the end of the design life.

Torque applied through the tightening mechanisms in the clamp bands creates tension in the band that produces the contact pressure. Factors influencing the amount of contact pressure generated include the diameter of clamp, the width of the contact zone, the efficiency and number of the tightening mechanism, the torque applied and the friction between the clamp band and elastomer.

Flexseal Clamping Mechanisms

Flexseal uses four types of stainless steel clamp bands throughout its product ranges. Stronger clamps are required as the coupling diameter increases.

Worm Drive Clamps

Worm drive mechanisms are used with two types of clamp and have fully perforated bands to allow self cleaning of any debris present on the clamps. Flexseal class these two types as medium and high duty clamps. Medium duty clamps are used for tightening torques of 6Nm. The high duty clamps are used when higher tightening torques are required and work at 10Nm and 13Nm.

Bolted Clamps

The third type of clamp replaces the worm drive with an M8 bolt and these are used on smaller diameter couplings requiring higher hydrostatic performance. A suitable lubricant is used on the bolt to reduce friction and increase the screw efficiency and also to prevent galling associated with stainless steel. These can be tightened up to 20Nm. These are used on small diameter Magnum Couplings.

The fourth type is a unique M8 mechanism designed by Flexseal for use with larger couplings. This provides a more robust and efficient mechanism that can be easily assembled and tightened on site. These clamping mechanisms are fitted to all Large Diameter Couplings and Magnum Couplings 600mm and above. They are utilised at 20Nm and 25Nm.

This design sets the bolt at a tangent to the coupling; optimising the conversion of the applied torque to tension in the band and so maximising the contact pressure between the seal and the pipe surface.

Both anchor points for the bolt are circular and their ability to rotate gives perfect alignment of the bolt as the clamp band is tightened.

All housing components are manufactured from Grade 1.4401 (316) stainless steel and the bolt thread is lubricated with grease that both reduces friction in the thread and prevents galling between the nut and the bolt.  This lubrication contributes to even distribution of the contact pressure around the full circumference of the coupling.  (This phenomenon is a characteristic of stainless materials).

Clamp Usage

The type of clamp used on the shear band will always match those used on the clamp bands.  The type of clamp band used for each product is listed below:-

Standard Couplings and Extra Wide Couplings (SC/SCW)

  • Standard couplings up to and including 180mm use medium duty worm drive clamps with a single housing
  • Size 200mm uses medium duty worm drive clamps with twin housings
  • Sizes greater than 200 and up to 620 use high duty worm drive clamps with twin housings

Large Couplings and Extra Wide Couplings (LC/LCW)

  • These couplings use the large bolted clamp and have two bolt mechanisms in the clamp bands

Magnum Couplings and Magnum Wraparound Couplings (MAG/MAGWRC)

  • These couplings use the small bolted clamp up to and including 699mm
  • Couplings larger than these use the large bolted clamp
  • All couplings have two bolt mechanisms on each clamp band

Wraparound Couplings (WRC)

  • Wraparound couplings less than 600mm use high duty worm drive clamps with twin housings
  • Larger wraparound couplings 600mm and above use the larger bolted clamp
  • All couplings have two bolt mechanisms on each clamp band

Drain Couplings (DC)

  • Drain couplings up to 250mm use medium duty worm drive clamps with a single housing
  • The 275mm version of the drain coupling uses high duty worm drive clamps with a single housing

Adaptor Couplings (AC)

  • All adaptor couplings that have nominal sizes 275mm and less use medium duty worm drive clamps with single housings. This covers up to and including model AC2756
  • Any adaptor couplings with one end having a larger size than 275mm use high duty worm drive clamps with single housings. The type of clamp used on each end of the adaptor coupling will always be the same

Euro Couplings (TC)

  • Medium duty worm drive clamps with single housings are used up to 265mm
  • Euro couplings larger than this use high duty worm drive clamps with single housings

Plumbing Coupling Range (PC/PAC)

  • All these couplings use medium duty worm drive clamps with single housings

Rubber End Caps (REC)

  • End caps up to and including 270mm use medium duty worm drive clamps with a single housing
  • Larger end caps use high duty worm drive clamps with a single housing

FA Saddles

  • Medium duty worm drive clamps with single housings are used on the FA150ST and FA 150B models
  • The FA200B has high duty single housing clamps fitted

Puddle Flanges

  • Moulded versions of the puddle flanges have medium duty worm drive clamps
  • The fabricated versions of the product use high duty clamps