Mason SLR Restrained Spring Mount for Wind and Seismic Loads

Overview

The Mason SLR is a restrained spring mount from Mason Industries, designed for equipment that must be isolated from the building structure but also held in place when its weight changes or when wind or earthquake forces act on it. Typical examples are cooling towers that lose their water weight when drained, chillers and condensers on roofs, and tall air handling units exposed to wind. Inside a rigid steel housing, one or more free-standing springs carry the load, while vertical limit stops with neoprene bushings stay out of contact during normal operation and only engage if the equipment tries to rise or is pushed sideways. The result is the vibration isolation of an open spring combined with the security of a restraint.

Seven Star LLC supplies the Mason SLR, the free-standing Mason SLF and SLFH mounts and Mason hangers to HVAC contractors, consultants and facility owners in Muscat, throughout the Sultanate of Oman and the GCC. Rooftop plant in the region faces strong seasonal winds, and many projects call for restrained isolators in their vibration specifications; we help match each Mason SLR size to the equipment weight and deflection in the schedule, with engineering support in Muscat.

Working Principle

As general engineering background, a spring isolator protects the structure by giving the supported machine a natural frequency well below its running frequency, so only a small fraction of the vibratory force passes into the floor. The static deflection of the spring sets that natural frequency, which is why consultants specify 1, 2, 3, 4 or 5 inch deflection depending on equipment speed and the stiffness of the floor. A free-standing spring, however, cannot stop equipment from lifting off when its operating weight is removed, and it offers no resistance to overturning forces from wind or seismic events.

The Mason SLR solves this by adding a restraint in parallel with the spring that is not in contact during operation. In the 100 Series the mount is shipped in a locked position with a spacer bar and restraining nuts; after the equipment is set and the adjustment bolts are turned to transfer load into the springs, the spacer bars are removed and the restraining nuts are set with a clearance of about 1/8 inch, so the spring works freely. If the equipment rises, the internal neoprene down stop and neoprene bushings cushion the contact. Mason publishes a maximum G rating for each 100 Series size so designers can check the restraint capacity, and its submittals note that designs resisting wind loads must follow ASCE 7-05.

Engineering Design of the Mason SLR

Each Mason SLR has a steel housing with a top plate that receives the equipment, color-coded springs seated on an internal neoprene acoustical pad, an adjustment bolt, vertical limit stops and an external non-skid neoprene friction pad under the base. When the mount is not used for seismic or wind resistance, bolting to the floor is not necessary because the friction pad holds it; when it is subject to seismic or wind forces it must be bolted or welded in position, and the friction pad is removed before welding. The submittals state that the mounts require level supports and that some equipment needs supplementary steel between the unit and the isolators.

The range covers several spring series. The 2 inch (51 mm) 100 Series runs from size 101 at 125 lb (57 kg) to size 118 at 40000 lb (18144 kg); 3, 4 and 5 inch series extend the choice for long-span roofs. Multiple-spring versions such as the Mason SLR-9, SLR-12 and SLR-16 group 9, 12 or 16 C or C2 springs under one top plate for heavy chillers and towers, with tapped holes for the equipment bolts. All 100 Series springs have additional travel to solid equal to 50% of the rated deflection, and the ratio of spring diameter to operating height is published for stability.

Key Features

Features of the Mason SLR described in the manufacturer’s submittal data sheets include:

• Free-standing springs inside a rigid housing that restrains the equipment against uplift and lateral forces.
• Vertical limit stops with neoprene bushings that are out of contact during normal operation.
• Internal neoprene acoustical pad and external non-skid neoprene friction pad to block high frequency noise.
• Shipping position with spacer bar and restraining nuts, so the equipment can be set at fixed height before release.
• Published maximum G ratings for each 100 Series size, for wind and seismic checks.
• Deflection series of 1, 2, 3, 4 and 5 inches to suit equipment speed and floor stiffness.
• Multiple-spring mounts with 9, 12 or 16 springs for heavy loads up to tens of thousands of pounds.
• Installation instructions and certification forms on every submittal sheet for site sign-off.

Industrial Applications

Cooling towers are the classic application for the Mason SLR because their weight drops sharply when the basin is drained, which would let an ordinary spring push the tower upward. Rooftop air-cooled chillers, condensing units, packaged air handlers, dry coolers and exhaust fans exposed to wind are other common uses, as are boilers and tanks whose contents change. On ground floors and in basements the same mount isolates pumps and generators where the consultant requires restraint for seismic design. The Mason SLR is normally specified alongside spring hangers on the connected piping, so the whole system moves together without loading the equipment nozzles.

In Oman and the GCC the Mason SLR is used under rooftop chillers and cooling towers on hospitals, hotels, universities, shopping centres and residential towers in Muscat, Sohar, Duqm and Salalah, and under district cooling equipment where consultants require restrained isolators. Seven Star LLC supplies the Mason SLR with the matching hangers, flexible connectors and inertia bases, and can help contractors interpret the deflection and restraint requirements in the vibration isolation specification.

Technical Specifications

The table below summarises Mason SLR data from the manufacturer’s submittal sheets; refer to the downloadable file for dimensions and the full ratings of each size.

How to Order

To order the Mason SLR, send Seven Star LLC the equipment weights, mount locations, required deflection and any wind or seismic design requirements, or simply the isolator schedule from your specification, and we will prepare a formal quotation. The manufacturer’s submittal data sheets can be downloaded from this page. Seven Star LLC supplies Mason vibration isolators in Oman and the GCC with engineering support in Muscat. Our team also supplies Rittal Blue e+ Wall-Mounted Enclosure Cooling Units for electrical enclosures, Belimo LF24-SR Spring-Return Damper Actuator 4 Nm, 2-10 V for air handling dampers and ABB ACQ580 Water and Wastewater Drive for pumps on the same projects.