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Pressure Performance

COUPLING PRESSURES

Flexible couplings are generally used in low pressure or gravity pipelines and sewers where the internal pressure likely to be experienced is very low. These pipelines normally run at atmospheric pressure and will only build up internal pressure if the pipe is blocked or running full. Consequently the pressure rating of the product is not usually an issue. There will be some installations where pressure is important (for instance pumped sewer lines or process plant) and the figures below can be used as recommended maximum working pressures. It should be noted that an increase in pressure is only likely to result in leakage of the seal and not outright failure of the product.

The manufacturing standard applicable to flexible couplings specifies testing that usually incorporates sealing against internal pressure. The tests also include some physical condition placed across the joint such as deflection, deformation and shear load. This is used to prove that not only will the couplings seal onto pipe surfaces but also they will be resistant to root penetration and that they can withstand movement due to ground settlement.

Standard BS EN 295:4

Products Covered: All couplings and bushes

Sizes Covered: Nominal sizes 100mm to 1000mm

Test Pressure: Internal pressure of 0.5 Bar

Standard WIS4-41-01

Products Covered: Shear banded couplings and bushes

Sizes Covered: Nominal sizes 100mm to 600mm

Test Pressure: Internal pressure of 1.0 Bar

Standard AS/NZS 4327

Products Covered: Strictly shear banded couplings and bushes but we have other couplings included in the schedule

Sizes Covered: Nominal sizes up to 600mm

Test Pressure: Internal pressure is related to size; 1.0 Bar up to 100mm - 0.35 Bar at 600mm

Standard KIWA BRL 5220

Products Covered: Strictly shear banded couplings and bushes but we have other couplings included in the schedule

Sizes Covered: Nominal sizes 100mm to 1300mm

Test Pressure: Internal pressure of 0.5 Bar

 

As a general rule we try to achieve a seal against 0.5 Bar internal pressure for all products.

Most testing is carried out with the pipes restrained from axial movement. Couplings should not be used to restrain pipe.

 

Vacuum

Some of the standards refer to vacuum testing and this is usually the preferred procedure for large couplings. Large volumes of water would be required and apart from the environmental aspect the weights involved make testing difficult.

Flexible couplings will withstand vacuum. The sealing mode is by compression of the rubber under the clamp bands. External pressure assists the seating of the rubber onto the pipe surface.

 

Recommended Maximum Working Pressures

COUPLING TYPE

COUPLING SIZES

INTERNAL PRESSURE – Bar

Standard Couplings

SC115-SC620

2.5

Wide Standard Couplings

SC225W-SC620W

2.5

Large Couplings

LC600-LC900

1.5

LC1000-LC1300

1.0

Wide Large Couplings

LC600W-LC900W

1.5

LC1000W-LC1300W

1.0

Magnum Couplings

MAG300

4.0

MAG400-MAG500

2.5

MAG600-MAG900

1.5

MAG1000-MAG1300

1.0

TC Couplings (Type 2A)

All Sizes

0.6

Wraparound Couplings

All Sizes

0.6

Drain Couplings

All Sizes

0.6

Adaptor Couplings

All Sizes

0.6

Plumbing Couplings

All Sizes

0.6

 

When non-shear banded couplings are pressurized internally they inflate. Backfill would prevent this from happening underground but this should be considered in any above ground installation.

 

Larger Couplings

Test data on couplings over 1300mm is very limited so no specific data is available. It would be expected that couplings up to 2000mm would seal against 0.5 Bar internal pressure but no guarantees can be given.

Bushes

Bushes will reduce the maximum pressure capability of the coupling. When bushes are utilised the maximum pressures stated should be those listed against the product standard and only then if a single bush is utilised. Limited testing has been carried out on multiple bush stacks. When an installation has two or three bushes we should only guarantee a watertight joint. Twin bushes with small shear banded couplings do have a greater capability but because of the limited testing this is difficult to quantify. (Typically a SC275 with two bushes can withstand 2.5 Bar internal pressure. An SC430 with a single 24mm bush leaked at 1.7 Bar. DN150 Multibush tested to 2.5 Bar).

Concrete

All the recommended maximum internal pressures are achievable when couplings are used with pipes having good surface finishes such as PVC, GRP and Clay. Concrete can be a very difficult surface to seal onto. Because of the variable nature of the concrete surface no pressure over those listed in the standard should be guaranteed.