WB Horizontal Thrust Restraints

It is not unusual to encounter problems where the horizontal combined air thrust exceeds 10% of the equipment weight. If the spring columns alone resist a 10% force, they will lean over about 12% of the rated deflection. This is the recommended maximum.

When the thrust is higher, the best solution is adding mass to bring the ratio back down to 10%. If adding mass is impractical, horizontal restraints are another possibility. This is particularly true of fan heads, but high pressure axial and centrifugal fans may present the same problem. The equipment may be hung or floor mounted. Our horizontal restraint is a modified spring hanger with a precompression adjustment to limit movement when the system starts and stops and the air pressure builds up or dies off, as explained in the specification.


When total air thrust exceeds 10% of the isolated weight, floor mounted or suspended air handling equipment shall be protected against excessive displacement by the use of horizontal thrust restraints. The restraint shall consist of a modified Specification B spring mounting. Restraint springs shall have the same deflection as the isolator springs. The assembly shall be preset at the factory and fine tuned in the field to allow for a maximum of 1/4”(6mm) movement from stop to maximum thrust. The assemblies shall be furnished with rod and angle brackets for attachment to both the equipment and duct work or the equipment and the structure. Restraints shall be attached at the center line of thrust and symmetrically on both sides of the unit. Horizontal thrust restraints shall be WB as manufactured by Mason Industries, Inc.