Grundfos CMBE TWIN Duplex Booster System

CMBE TWIN is two CMBE pumps mounted on a common manifold with the control already set up for duplex operation — lead/lag alternation, automatic changeover and shared run time, without anyone configuring a panel in the field.

That buys two things at once. Twice the water at the same pressure as the single pump it is built from, and standby capacity — one pump can be taken out of service and the building stays in water. For a hotel, a small commercial building or anywhere downtime is not acceptable, that second point is usually the reason for the purchase.

Three models, each built from a matching CMBE single: TWIN 1-44, TWIN 3-51 and TWIN 10-54.

Combined flow and shut-off are read from the two-pump axis of the Grundfos CMBE TWIN chart, which publishes both scales on the same curve — these are not doubled from a single-pump figure. Motor data is Grundfos’ one-pump electrical table. All three models connect to a fuse box with 15 ft of cable and no plug.

Grundfos plots CMBE TWIN on one chart with two flow scales — one pump and two pumps — against the same head. The tables below are read from the two-pump scale, so they are published duplex figures rather than a single-pump curve doubled. Every value is the pressure the system adds on top of the inlet.

CMBE TWIN 1-44 — both pumps running

CMBE TWIN 3-51 — both pumps running

CMBE TWIN 10-54 — both pumps running

Two pumps hold more pressure at the flow the building actually draws. Each pump carries half the water, so each sits higher on its own curve, and the gain is large. Read it off the same chart: 60 GPM from a single CMBE 10-54 comes out at 31.9 psi added, while 60 GPM split across the two pumps of a TWIN 10-54 comes out at 54.4 psi. On the TWIN 3-51, 24 GPM is 27.3 psi from one pump and 62.0 psi from two. The shut-off ceiling at zero flow is the one figure that does not rise, because it is set by the pump build — 79.2 psi on the 10-54, 73.8 psi on the 3-51.

Size the set so one pump can carry the building. On a duplex bought for redundancy, the design flow should sit inside what a single pump delivers — otherwise losing a pump means losing pressure, which defeats the reason for buying two.

Fed by a city main — the system adds on top of what already arrives, and the drive only makes up the difference between the main and your setting. Incoming pressure buys you more flow, not more pressure.

Best operating range, both pumps running: 15 to 22 GPM on the TWIN 1-44, 21 to 30 GPM on the TWIN 3-51, and 74 to 106 GPM on the TWIN 10-54. This is where the system turns the most electricity into water pressure. Ask for more flow than it can deliver at your setting and both pumps run at full speed continuously, which is where motors and seals wear out. Sizing a booster to the building rather than to the headline numbers is what makes it last.

Zero flow is the shut-off point — a ceiling, not a working point. Figures are at full drive speed; the drive holds lower pressures by running slower, and cascade control brings the second pump in only when the first cannot meet demand. Grundfos publishes CMBE TWIN performance as a plotted chart with no accompanying duty table, so these figures are read from the published curve and rounded down where the reading is uncertain; nothing is extrapolated past the drawn range. Best operating ranges are derived by us from that curve, not stated by Grundfos. For a certified duty point, call 1-888.510.4036 and we will request the factory submittal. Source: Grundfos CMBE & CMBE TWIN Data Booklet 98647967 (10.2025), chart TM090949, printed page 21, ISO 9906:2012 3B.

The Grundfos GO app does not connect to the system on its own — it needs the Grundfos MI 301 mobile interface, which is sold separately. The MI 301 is a pocket-sized module that pairs to your iOS or Android phone over Bluetooth Low Energy and then reaches the pumps by radio or infrared. Without it, the app cannot see the system — the CMBE TWIN still runs and the pressure set point is still entered on the operating panel, but everything below requires the module.

With the MI 301 connected, the free Grundfos GO app gives you setup, status overviews, technical product information and live operating parameters from your phone. Each CMBE pump on the TWIN connects to Grundfos GO through the module, so commissioning takes minutes and no laptop. Add the Grundfos MI 301 to your order.