Gorman-Rupp RD4 Roto-Prime Petroleum Transfer Pump

The Gorman-Rupp RD4 is the 6 x 4 inch double-volute model of the Roto-Prime RD Series, a priming-assisted centrifugal pump designed for petroleum products, petrochemicals and solvents. A variable-capacity vane priming pump automatically evacuates air and vapour, which is why Roto-Prime units are used for loading and off-loading road tankers and stripping product from the suction line without spillage of volatile liquid.

The vane-priming principle

During priming, a vacuum is created while the sliding-vane priming pump is in pumping mode. Vapour flows from the suction to the priming pump through balance holes in the impeller and a kidney-shaped hole in the body cover, and is discharged through tubing from the bearing housing to the volute discharge flange downstream of the integral priming valve, so it cannot return to suction. Once the centrifugal stage builds pressure, the priming valve opens and discharge pressure acts on the slide block, moving the priming pump to a neutral position where it saves vane wear until air or vapour appears again. The result is a pump that does not vapour-lock and can run with air present at start-up or after loss of suction.

Technical specification

RS or RD: choosing the series

Roto-Prime comes in two styles. RS models are standard duty, single volute at 1750 rpm; RD models are for higher head, double volute at 3450 rpm. The RD4 is the highest-head size in the range at 390 ft, so it is the one to consider for long discharge lines, truck loading arms and elevated storage. Other sizes are compared below.

Options and accessories

Optional items named in the brochure include stainless steel pump rotor shafts and exposed fasteners, bronze impellers, an iron rotor for the priming pump and the GRP33-08 air release valve with a stainless steel float to evacuate suction-line air and keep positive self-priming against moderate to high static heads. Optional seals can be specified for different liquid formulations. The brochure describes the line as globally accepted and widely used by major oil companies for clean product transfer; it lists no hazardous-area approvals, so ask the manufacturer when the unit will be installed in a classified area.

Duty point in other units (derived)

Unit conversions below are calculated from the printed maximum values and are not manufacturer statements.

For terminal and depot work, note the difference in duty between RD and RS: the RD4 is rated for 390 ft at 3450 rpm while the 6 x 5 inch RS5 is the high-flow standard-duty choice at 1480 GPM. Because the priming pump idles in neutral once prime is established, vane wear is limited to the periods when air or vapour is actually present. Specify the liquid, vapour pressure, temperature and the seal elastomer when ordering.

Support literature and ordering notes

The manufacturer states that manuals with parts lists, specification data sheets, performance curves and outline drawings are available in PDF and CAD formats for every pump, and that parts are normally shipped within 24 hours. For Roto-Prime, the key ordering inputs are the liquid and its vapour pressure, flow and head, the impeller and housing materials (aluminium impeller and ductile iron or cast steel housing are listed), the seal elastomer and the drive speed. Base-mounted motor-driven units are the configuration shown in the brochure.

Frequently asked questions

What liquids is Roto-Prime designed for?

Petroleum products, petrochemicals and solvents, per the brochure.

How does it avoid vapour lock?

A variable-displacement vane priming pump removes air and vapour automatically and shifts to neutral once liquid pressure builds.

What are the RD4 limits?

930 GPM (59 lps), 390 ft (119 m) head and 0.50 in (13 mm) solids.

What speed does the RD Series run?

3450 rpm for double volute RD models, 1750 rpm for single volute RS models.

Is gearbox needed?

No. The pumps operate at synchronous speeds, eliminating the need for gearboxes.

Documents and quotation

Brochure: Roto-Prime (AV-05970). More products: Pumps. Seven Star LLC supplies from Muscat as an independent supplier; send liquid, temperature and flow for a quotation.