Mason SLFH Free-Standing Spring Mount with Bolt-Down Baseplate

Overview

The Mason SLFH is a free-standing, unhoused steel spring mount made by Mason Industries for isolating vibration and noise from mechanical equipment. It belongs to the Type SLF family, one of the most widely specified spring isolators for HVAC plant rooms, and differs from the standard SLF only by its baseplate, which has two or four holes so the mount can be bolted to the supporting structure. Mason developed the SLF design after concluding that springs running inside guided housings tended to bind when cocked and transmitted horizontal vibration; removing the housing and designing the spring itself as a stable column gave better isolation in both the vertical and horizontal directions.

Seven Star LLC supplies the Mason SLFH, the standard SLF and the related Mason restrained mounts and hangers to mechanical contractors, consultants and facility owners in Muscat, across the Sultanate of Oman and the wider GCC. We help project teams match the mount size and deflection to the equipment schedule in the consultant’s vibration isolation specification, and keep engineering support in Muscat for HVAC and pumping projects.

Working Principle

As general engineering background, a spring isolator works by giving the supported machine a natural frequency well below the frequency of the disturbing force. The static deflection of the spring under load sets that natural frequency: the larger the deflection, the lower the frequency and the higher the isolation efficiency at a given running speed. Slow machines and equipment on long-span floors therefore need springs with more deflection, while fast machines on grade can use shorter springs. Steel springs isolate low frequency vibration very well but can pass high frequency noise along their coils, which is why a resilient pad is placed in series with the spring.

The Mason SLFH applies this principle with a spring designed for stability. According to the Mason bulletin, horizontal spring stiffness can be made as high as, or even higher than, vertical stiffness by controlling the ratio of the spring’s compressed height to its mean coil diameter and the ratio of static deflection to compressed height. Mason specifications suggest a minimum ratio of 0.75 between spring diameter and compressed height. All springs have additional travel to solid equal to 50% of the rated deflection, so the solid height equals the free height minus 1.5 times the rated deflection; this keeps the springs in a low stress range and absorbs errors in load assignment. The springs are designed not to exceed their elastic limit when compressed solid, so an overloaded spring returns to its free height.

Engineering Design of the Mason SLFH

Each Mason SLFH consists of one or more color-coded springs seated in a ferrous cup with a molded non-skid neoprene acoustical cup or pad underneath. A substantial adjustment bolt at the top loads the spring and maintains the free and operating height; its head is the equipment supporting surface, and it is tapped to take a locking cap screw that secures the equipment base or a Mason height saving bracket. This arrangement makes it easy to remove an isolator for servicing. The bulletin notes that 5 inch (127 mm) springs are sometimes furnished with three adjustment bolts in a tripod arrangement, and that pull-down brackets or oversized bolts are other stabilizing methods for large deflections.

The difference between the SLF and the Mason SLFH is the bolt-down baseplate. Mason points out that bolting a mount tends to bypass the acoustical action of the neoprene pad and adds installation cost, so it recommends the plain SLF unless the SLFH must be used, for example on elevated installations on steel beams. The Mason SLFH is not offered with the light X-series springs. A standard Mason SLFH has a painted or powder coated finish, springs are powder coated or zinc electroplated, and mounts can be made in stainless steel or hot dip galvanized at additional cost, an option worth considering for coastal and rooftop installations in Oman.

Key Features

The main features of the Mason SLFH spring mount taken from the manufacturer’s bulletin are:

• Unhoused spring design that cannot bind and isolates horizontal as well as vertical disturbances.
• Nominal deflection series of 1, 2, 3, 4 and 5 inches (25, 51, 76, 102 and 127 mm).
• Additional travel to solid equal to 50% of the rated deflection on standard springs.
• Baseplate with two or four bolt holes for fixing to steel beams, frames or concrete plinths.
• Molded non-skid neoprene acoustical cup or pad to block high frequency noise.
• Adjustment bolt with locking cap screw that maintains free and operating height.
• Matching Mason height saving brackets to lower the overall height of the equipment base.
• Single spring sizes and multiple spring mounts with 2, 3, 4, 6, 9, 12 or 16 springs for heavy loads.

Industrial Applications

The Mason bulletin shows SLF and SLFH springs under belt driven centrifugal fans on steel or concrete bases, utility sets, factory assembled air handling units, end suction and double suction pumps on concrete inertia bases, vertical pumps, directly driven refrigeration compressors, belt driven and tank type air compressors, and slow speed reciprocating compressors on inertia blocks. When a Mason SLFH installation is planned, mounts of different capacities but the same deflection are used at each end of a machine to give uniform deflection. Where a fan head creates high horizontal thrust, Mason recommends horizontal thrust restraints or a heavy concrete base, and where equipment is exposed to wind or seismic loads a restrained mount such as the Mason SLR should be used instead of the Mason SLFH.

In Oman and the GCC the Mason SLFH is typically specified under chilled water pumps, condenser water pumps, air handling units and fans in hospitals, hotels, malls, office towers and district cooling plants in Muscat, Duqm, Sohar and Salalah, where plant rooms often sit above occupied floors. Seven Star LLC supplies the Mason SLFH together with the inertia bases, hangers and flexible connectors that complete an isolation package, and can help contractors check that the selected deflection matches the consultant’s equipment schedule.

Technical Specifications

Key data for the Mason SLFH and the related SLF ranges from Bulletin SLF-200-8 are summarised below; consult the bulletin for the full spring and dimension tables.

How to Order

To order the Mason SLFH, send Seven Star LLC your equipment schedule with operating weights, running speeds and the required static deflection, or the isolator tags from the consultant’s specification, and our team will prepare a formal quotation. The manufacturer’s bulletin is available as a datasheet download on this page. Seven Star LLC supplies Mason vibration isolators in Oman and the GCC with engineering support in Muscat; contact our engineering team for selection support, related items such as Belimo LF24-SR Spring-Return Damper Actuator 4 Nm, 2-10 V and Rittal Blue e+ Wall-Mounted Enclosure Cooling Units for HVAC packages, and drives such as ABB ACQ580 Water and Wastewater Drive for the pumps you are isolating.