According to NFPA 20 (Section 6.4.3), centrifugal pumps must be securely attached to a solid foundation to ensure proper alignment between the pump shaft and the driver shaft.
Here is a breakdown of the general rules of thumb for sizing your pads, followed by a few manufacturer-specific requirements you need to catch before the concrete cures.
The Golden Rules of Sizing
The foundation must be substantial enough to absorb vibration and provide permanent, rigid support for the baseplate. When sizing a concrete plinth for a skid-mounted horizontal, end-suction, or in-line fire pump, follow these baseline guidelines:
Weight: The concrete pad should weigh 2 to 3 times the combined weight of the pump and motor assembly.
Dimensions: Extend the pad at least 6 inches beyond the skid baseplate on all sides. (Some manufacturers recommend going up to 12 inches wider).
Material: Use a reinforced concrete mix. A standard 1:2:3 mixture (Cement : Sand : Aggregate) with a maximum 4-inch slump and a 28-day compressive strength of 1,750 psi is highly recommended.
Reinforcement: Use layers of 6-inch square No. 8 gauge steel wire fabric (or equivalent), placed horizontally 6 inches apart.
Example:
Pump/motor weights approx 365-lbs x 5 = 1,825 lbs.
1,825 lbs / 150 lbs. per cubic foot of concrete = 12 cubic feet of concrete.
Manufacturer-Specific Requirements
While the rule of thumb gets you close, the brand of the pump dictates the exact anchoring strategy. Always check your certified outline drawings, but keep these manufacturer quirks in mind:
Aurora Pumps
The foundation should have a level surface and have sufficient mass to prevent vibration and form a permanent rigid support for the unit. The most satisfactory foundations are concrete with anchor bolts of adequate size embedded in the foundation in pipe sleeves with an inside diameter 2½ times larger than the bolt diameter. This will allow final accurate positioning of the unit
Armstrong Pumps
Foundation should be sufficiently substantial to absorb any vibration and to form a permanent, rigid support for the base plate. Foundation bolts of suitable size should be embedded in the concrete located by a drawing or template. Place pumping unit on foundation with wedges under base plate leaving approximately 3/4” space for grouting. Carefully level the unit by adjusting the wedges until shafts of pump and driver are leveled, recreating factory alignment. Check coupling faces as well as suction and discharge flanges of pump for horizontal or vertical position with a level. Slight misalignment at this point may be corrected by adjusting the wedges
Xylem Pumps
A pump should have adequate space for operation, maintenance, and inspection. Sub Base mounted pumps are normally grouted on a concrete foundation, which has been poured on a solid footing. The foundation must be able to absorb any vibration and to form a permanent, rigid support for the pumping unit. The foundation must be of adequate strength to support the complete weight of the pump, plus the weight of the liquid passing through it. A typical installation will have bolts with a pipe sleeve 21/2 times the bolt diameter embedded in the concrete, sized and located in accordance with the dimensions given on the Pump Certified Outline Drawing, if provided. The pipe sleeve allows movement for final positioning of the foundation bolts to conform to the holes in the Sub Base flange.
Remove water and/or debris from anchor bolt holes/sleeves prior to grouting. If the sleeve type bolts are being used, fill the sleeves with packing or rags to prevent grout from entering. Carefully lower the Sub Base onto the foundation bolts. Hand tighten the bolt nuts. Leveling the Sub Base may be done by several methods.
When the pump is mounted directly on a structural steel frame, pumps shall be located directly over, or as near as possible to the main building members, beams, or walls. be bolted to the support to avoid distortion, prevent vibration, and retain proper alignment. If a Sub Base is being bolted to a structural steel foundation, or the Sub Base is not grouted to the concrete foundation, use shims for leveling the plate
SPP Pumps
A foundation plinth should be constructed to support each pumpset on a floor area free from expansion joints. These foundation plinths should be sufficiently substantial to absorb vibrations and rigid enough to avoid any twisting or misalignment. As a rough guide, they should be at least 12 inches wider than the pumpset on all sides and weigh between 1 and 1.5 times the weight of the pumpset. Plinths for fire pumps are recommended to have a minimum height of 300mm but height should be sufficient to achieve the necessary weight and to accommodate the pockets for fixing bolts. Foundation height may be calculated thus:
Use a suitable concrete mixture by volume is 1:2:3 (Cement : Sand : Aggregate) with a maximum 4.00 inches slump, and a 28 day compressive strength of 1,750 tonf/in2
The foundation should be reinforced with layers of 6.00 inche square No.8 gauge steel wire fabric, or equivalent, horizontally placed 6.00 inches apart. Foundation concrete should be poured without interruption to within 1.00 inch of the finished height.
The top surface should be well scored and grooved before the concrete sets to provide a bonding surface for the grout. The foundation should be allowed to cure for several days before installation of the baseframe.
Foundation Bolts: Two types of foundation bolts are normally used; either rag bolts set into pre cast pockets in the plinth or, chemical anchor bolts for which pockets are drilled into the plinth after casting
Patterson Pumps
The foundation should be sufficiently substantial to absorb vibration and to form a permanent rigid support for the pump. Concrete is most widely used for foundations. Before pouring a foundation, locate anchor bolts per the outline drawing. Anchor bolts should be installed in sleeves twice the anchor bolt diameter to allow for alignment with the holes in the soleplate or discharge head. Allow for 3/4 inch to 1-1/2 inches of grout between foundation and discharge head or soleplate. The top surface of the foundation should be roughened to provide a good bond for the gro
LEVELING THE UNIT: Position the unit so the anchor bolts are aligned in the middle of the mounting holes in the base. Place metal shims or metal wedges directly under the part of the base carrying the greatest weight, and space them close enough to give uniform support and stability. Adjust the metal shims or wedges until the top flange of the discharge head is level. Tighten the foundation bolts snugly, but not too firmly, and recheck the alignment before grouting.
The Final Step: Alignment and Grouting
Do not fully tighten your foundation bolts until the grout has completely hardened—usually about 48 hours after pouring.
Before grouting, the top surface of the concrete should be scored and grooved to provide a strong bonding surface. Once you have leveled the baseplate using shims or wedges and verified the alignment, completely fill the baseplate with grout. It’s best practice to leave the leveling shims permanently grouted in place.
Getting the foundation right on the front end prevents massive headaches during commissioning and ensures your pump curves look exactly the way they are supposed to during testing. If you have questions about specific dimensions or need certified outline drawings for your next build, reach out to our team.