Curbs and Bases
Custom Built Spring Curbs and Rails
P & R Series
1.00 - 3.00" Deflection
P Series curbs and R Series rails are high quality, fully adjustable support systems specifically designed for rooftop unit vibration isolation and seismic/wind restraint. Each custom-built unit incorporates both the roof curb and spring isolation into one complete structure. VMC engineers design each curb and rail to custom fit any rooftop mechanical equipment.
Spring deflections up to 3” can be specified to compensate for large floor spans, and spring pockets are positioned within the curb at the correct load points for proper support and seismic restraint. All spring pockets incorporate a minimum 1/4” elastomeric cup or pad in series with the spring to provide optimum isolation efficiency.
These fully flashable rooftop support systems also save the contractor unnecessary labor costs. The curb and rooftop unit can be fully installed and adjusted before the roof is sealed, eliminating the possibility of any damage to a finished roof.
Leveling of the rooftop unit is accomplished easily as all spring pockets are accessible from around the outside of the curbs. All springs are color-coded for ease of identification, and any spring can be removed and replaced with the rooftop unit installed. Once adjusted and leveled, the rooftop unit becomes free floating - completely isolated from the building structure, while completely restrained to it.
The P Series roof curbs and R Series rails are fabricated from force-resisting structural steel specifically designed to withstand seismic and high wind forces. Unlike standard curbs that typically come with a rooftop air handling unit, or sheet metal curbs incorporating a seismic isolator, the VMC rooftop support systems combine our seismic spring design within a moment resisting frame. Our high strength frame is capable of direct, positive attachment to both the building structure and the roof mounted equipment while each spring pocket provides vibration isolation and both seismic and wind restraint.
Standard sheet metal curbs that typically come with rooftop equipment are not capable of resisting these forces and do not allow for direct, positive attachment to the roof structure and mechanical equipment. Our high strength frame can be bolted or welded to the roof structural steel and absolutely will not break away during an earthquake or high wind forces. Sheet metal curbs cannot accept point loading of these forces and will tear away from the building structure due to their thin construction.
Custom-Built Iso-Curb Spring-Flex Bases
AXR Series
1.00" Deflection
The AXR Series are spring isolation bases designed to protect curb-mounted rooftop equipment from the building structure. These bases are built to mount between the rooftop equipment and the existing roof curb – providing excellent vibration isolation with uniform spring deflection along the entire perimeter.
The AXR Series are a one-piece unitized construction that is custom-sized to fit the exact dimensions of rooftop equipment. The bases are fabricated from extruded aluminum upper and lower frames with zinc electro-plated springs placed between the two frames.
The springs are mechanically fastened, sized and positioned within the frames to ensure a uniform 1” static deflection for the entire system. A continuous, flexible “Hydro-Gard” seal is attached between the upper and lower members, and a continuous closed cell elastomeric gasket is bonded to the top and bottom surfaces to provide an airtight and watertight seal.
The AXR Series can be supplied with section dividers for installations where ductwork requires a provision for supply and return lines.
Concrete Inertia Bases
Model:MPF/WPF Series
The MPF (modular pouring forms) and WPF (welded pouring forms) are designed for use with mechanical equipment that requires a concrete inertia base. The MPF/WPF Series are sturdy frames that, when filled with concrete, provide an effective means to isolate vibration and limit the motion of any demanding equipment – large pumps, fans, motors and compressors.
VMC MPF Series inertia bases should be used with pumps, fans having a 40” wheel diameter and larger, centrifugal fans driven by motors of 75 Hp or larger, and certain types of compressors. This type of equipment usually possesses low rotational speed, high static pressure, or a large unbalanced force, which cannot be attenuated by the use of springs alone. The benefits of using an inertia block include the addition of mass to the isolated system, which reduces movement. For example, if a 1000 lb. machine develops 100 lb. of unbalanced force, the machine would displace “X” inches. However, if you mount the machine to an inertia base weighing 1000 lb., the same 100 lb. unbalanced force must now move 2000 lb. The displacement has been reduced by 50%. VMC inertia bases also lower the center of gravity of the isolated system – offering greater stability and a rigid base for the equipment to help maintain alignment.
The MPF series feature a modular, bolt-together design that can be shipped assembled or knocked-down for field assembly. The WPF types feature a sturdy, welded design complete with reinforcing rods (rebar) welded in place.
Custom-Built Wide Flange Bases
WFB/WFR Series
0.50-5.00" Deflection
VMC manufactures a complete line of fan and motor bases that should be specified for all belt driven centrifugal fans that do not require a concrete inertia block. Available with an adjustable motor slide rail, VMC WFB Series bases are designed to maintain proper drive alignment and resist starting torque without the use of restraining snubbers.
Whenever mechanical equipment lacks the proper rigidity for point support, VMC WFR Series rails should be utilized. Like our bases, WFR Series rails are available in wide flange, angle, or channel steel and can be designed for use with any isolator in our product line.
When an equipment submittal drawing is provided to the VMC Engineering department, a properly designed base or rail drawing, indicating isolator model numbers is produced for customer approval. Once approved, drawings are provided to our manufacturing department for fabrication and shipment.
