A.Y. McDonald DuraMAC Dual-Mode Duplex Booster Pump

The Dual-Mode Duplex puts two pumps on one stainless steel base with a 20 gallon pressure tank and 2 in NPT manifolds with ball valves. It is designed for lead/lag: the lead pump is set higher than the lag, and if the lead cannot keep up and pressure falls to the lag setpoint, the second pump starts and the two run together. It can be set so that either pump alone satisfies demand, which is full redundancy.

That makes it the configuration for larger apartment complexes, factories and process work, and commercial buildings where downtime is not acceptable or demand spikes above what one pump can handle. Stainless steel and no-lead brass waterway, dry-run protection, electronics separated and sealed from the waterway.

Two pumps carry more water — 120 GPM against 70 GPM for one — and hold more pressure at the flow the building actually draws. Each takes a share of the flow, so each sits higher on its own curve. At 70 GPM a single 60 PSI pump adds 10 psi; this Duplex, with both pumps running, adds 41 psi at the same flow. The 44 PSI set goes from 19 psi to 33 psi.

Either pump can be set to satisfy demand alone, so the building keeps running if one goes down. The shut-off ceiling at zero flow stays at the model’s boost, 60 or 44 psi. The same pump is also offered as a Simplex on a base with a tank, and as a Modular without base or tank.

Single-pump figures from the published curve on p. 243; Duplex figures from A.Y. McDonald’s published curve with both pumps running, p. 245 (Baker Water Systems DuraMAC Booster Pumps catalog, rev 3/26), rounded down.

The figures below are the pressure this system adds with both pumps running. That is what a pump curve measures — the impeller does not know what pressure is already on its inlet.

Models

Source: Baker Water Systems DuraMAC Booster Pumps catalog, rev 3/26, p. 245. Amps are as published per pump. PRV: A.Y. McDonald recommends a pressure reducing valve above this incoming pressure, so total boosted pressure stays below 80 psi. Many plumbing codes do not recommend system pressure above 80 psi; check local code.

Pressure added in PSI, both pumps running, by system flow

Drawing from a tank or cistern — nothing arrives with pressure, so what the pump adds is what you get. Read the table straight through: the 60 PSI model delivers about 80 GPM at 36 psi with both pumps running.

Fed by a city main — these are single-speed pumps, so the boost arrives on top of whatever the main already delivers. A.Y. McDonald recommends a pressure reducing valve above 36 psi incoming on the 44 PSI model and above 20 psi on the 60 PSI model, so that total boosted pressure stays below 80 psi.

Best operating range: 60 to 110 GPM with both pumps running. Below this range the pump recirculates internally, which causes vibration and premature seal wear. Above it, it cavitates and the motor draws past its rating. Most booster failures are pumps that were oversized for the building.

Zero flow is the shut-off point — a ceiling, not a working point, and the same figure as a single pump because it is fixed by the model. The table ends at the published maximum, 120 GPM. Figures are 60 Hz US data at full speed with both pumps running, digitized from A.Y. McDonald’s published Duplex curve in the Baker Water Systems DuraMAC Booster Pumps catalog, rev 3/26, p. 245, and rounded down. Best operating range is derived from the published curve; A.Y. McDonald publishes no efficiency curve for these models. Feet of head = PSI × 2.31.

Same pump, same motor, same dual-mode control in all three. What changes is what comes with it and how much water it carries. You are looking at the Duplex.

Figures from the Baker Water Systems DuraMAC Booster Pumps catalog, rev 3/26, pp. 241–246.

The DuraMAC Dual-Mode control runs in two modes. It is a different control from the three-mode unit fitted to the Residential and Light Commercial boosters.

Pressure Mode — starts on pressure drop, stops on low flow. The control measures pressure with a transducer and starts the pump at an adjustable start pressure point. The pump stops when flow falls below three gallons per minute. A preset seven-second delay after flow stops fully pressurizes the system and eliminates water hammer.

Flow Mode — starts and stops on flow, regardless of pressure. Use it where there is minor leakage or where incoming pressure varies. Starting flow is approximately five gallons per minute; the pump stops when flow falls below three.

Parts in contact with the water, per the Baker Water Systems DuraMAC Booster Pumps catalog, rev 3/26.

Seals, impellers, controls and other service parts for this pump are listed on DuraMAC Booster Pump Parts — 70 GPM Commercial, by part number.