Mason ND Double Deflection Neoprene Mount

Overview

The Mason ND is a double deflection neoprene mount made by Mason Industries for isolating noise and vibration from light and medium mechanical equipment. It is a compression type rubber mounting with a steel base plate and a tapped steel top insert, both completely covered in molded neoprene, and is supplied with its cap screw and washer. Where steel springs are chosen for low frequency isolation, neoprene mounts like the ND are chosen for high frequency noise control and for smaller, faster machines where a modest static deflection is enough. Mason, which started in 1958, explains in its bulletin that it now sells only the double deflection ND, rather than a single deflection version, so that every customer has the benefit of the better product.

Seven Star LLC supplies the Mason ND together with Mason spring mounts, restrained mounts and hangers to HVAC contractors, maintenance teams and consultants in Muscat, across the Sultanate of Oman and the GCC. We help select the Mason ND size and durometer from the equipment weight per mounting point, with engineering support in Muscat.

Working Principle

Rubber mounts isolate vibration in the same way as springs: the mount deflects under the static load, giving the supported machine a natural frequency below its disturbing frequency. As general engineering background, rubber has internal damping and does not carry high frequency noise along its body the way a steel coil can, so it is very effective against structure-borne noise. Its limitation is deflection, because rubber can only be compressed a fraction of its height, so neoprene mounts give lower isolation efficiency than springs on slow machines.

The Mason bulletin describes how early rubber mountings were loaded in shear and could fail at the bond between rubber and metal, bottoming out when overloaded. Compression mountings cost less for a given capacity and still provide a cushion if overloaded, and when loaded conservatively their load deflection curve is similar to a straight line shear curve. The Mason ND uses two rubber elements in series within one molded part, which roughly doubles the deflection of a single mount; Mason states that ND mounts offer more than three times the deflection of pads, and the ratings table shows rated deflections of 0.35 to 0.50 inch (9 to 13 mm) with straight line deflection curves.

Engineering Design of the Mason ND

Each Mason ND has a rectangular steel base plate with two bolt holes and a round neoprene body rising to a tapped top insert. The neoprene covers all steel surfaces to prevent corrosion, and molded friction surfaces at the top and bottom mean that bolting to the floor is unnecessary in most installations; the mounts can be used under flat bases with no bolt holes in much the same way as rubber pads. When the equipment has a flush drain pan or tank on the bottom, the mount can be inverted so that the rubber covered base plate supports the equipment over a large area. Standard mounts are molded in oil resistant neoprene, and because Mason molds them itself, bridge bearing quality neoprene, natural rubber or other elastomers can be supplied.

The range comprises five sizes, ND-A, ND-B, ND-C, ND-D and ND-DS, with color marks indicating the durometer of the rubber. Softer 30 and 40 durometer compounds carry light loads with more deflection, and 60 and 70 durometer compounds carry heavier loads; the largest ND-DS in 70 durometer is rated from 2150 to 4300 lb. Each size has a published cap screw and maximum bolt diameter, from 5/16 inch on the ND-A to 1/2 inch on the ND-C, ND-D and ND-DS. Mason’s specification text for the Mason ND calls for a minimum static deflection of 0.35 inch (9 mm), neoprene covered metal surfaces and friction pads top and bottom.

Key Features

The Mason ND features listed in the manufacturer’s bulletin are:

• Double deflection compression design in a single molded mounting.
• More than three times the deflection of isolation pads.
• Effective control of noise and high frequency vibration.
• Neoprene covering over all steel parts to prevent corrosion.
• Bonded bottom friction surface and top rubber washer, so bolting is unnecessary in most installations.
• Cap screw and washer supplied with every mount.
• Oil resistant neoprene as standard, with bridge bearing neoprene, natural rubber or other elastomers available.
• Straight line deflection curves and color-coded durometers for simple selection.

Industrial Applications

Neoprene mounts suit equipment where the consultant’s schedule calls for a small deflection: in-line and small end suction pumps, fan coil units, small air handling units, exhaust and ventilation fans, packaged condensing units, small transformers, compressors on rigid bases and electrical or instrument panels mounted near vibrating machinery. They are also used under equipment on ground-bearing slabs where steel springs are not needed. The Mason ND can be specified as the isolation element within larger assemblies, and the Mason range includes neoprene hangers with similar elements for suspended fans and ducts.

In Oman and the GCC the Mason ND is commonly specified for mechanical rooms in hotels, hospitals, schools, offices and residential buildings in Muscat, Sohar, Nizwa and Salalah, as well as for pump skids and ventilation equipment in industrial plants. The neoprene covering is helpful in humid coastal plant rooms. Seven Star LLC supplies the Mason ND alongside Mason spring isolators, helping contractors meet the vibration isolation schedule with one coordinated package.

Technical Specifications

The following data for the Mason ND are taken from the Mason bulletin and submittal sheet; see the downloadable files for full dimensions.

How to Order

To order the Mason ND, send Seven Star LLC the equipment list with weights per mounting point and any deflection requirement from the specification, and we will prepare a formal quotation. The Mason bulletin and submittal sheet are available as downloads on this page. Seven Star LLC supplies Mason vibration isolators in Oman and the GCC with engineering support in Muscat; we also supply related equipment such as Belimo LF24-SR Spring-Return Damper Actuator 4 Nm, 2-10 V, Rittal Blue e+ Wall-Mounted Enclosure Cooling Units and ABB ACQ580 Water and Wastewater Drive for building services projects.