Grundfos CMBE Constant Pressure Booster

CMBE is a complete constant-pressure booster built around a horizontal multistage CM pump with a variable frequency drive integrated into the motor, a pressure sensor and a 0.53 gallon diaphragm tank. The drive varies speed to hold one discharge pressure as demand moves, so the system does not cycle between cut-in and cut-out.

Ten hydraulic builds across four flow families. CMBE 1 runs to 14.5 GPM, CMBE 3 to 26.4 GPM, CMBE 5 to 35.2 GPM and CMBE 10 to 70.4 GPM. The first number in the model name is the flow family; the second is Grundfos’ nominal head in metres for that build, which is close to but not the same as the shut-off pressure on the curve. Flow and pressure are chosen separately, which is the point of the naming.

CMBE runs on a flooded or pressurised suction. Grundfos states a maximum suction lift of 1 m (3.3 ft) including inlet pipe loss at 68°F, and the unit is not self-priming. Where the source sits further below the pump, the SCALA1 and SCALA2 self-prime to 26 ft.

Grundfos builds the two-pump version at the factory as the CMBE TWIN — the same hydraulics on a common base and manifold, with cascade control and automatic alternation already configured. It doubles the water available at the same pressure and leaves a spare machine on site, and it is chosen at purchase rather than assembled later.

Two pumps hold more pressure at the flow the building actually draws, because each carries half the water and sits higher on its own curve. Grundfos publishes both cases on one 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. The shut-off ceiling at zero flow is the one figure that does not rise, because it is fixed by the pump build.

Shut-off is what the unit holds at zero flow — a ceiling, not a working point. Grundfos plots the CMBE range on one family chart and does not draw every model down to zero flow; where the low-flow end is not drawn, this table says so rather than extrapolating it. Best operating ranges are derived by us from the published curve (water horsepower peaks, and best efficiency sits left of that peak); Grundfos does not state them. Source: Grundfos CMBE & CMBE TWIN Data Booklet 98647967 (10.2025), performance chart TM090716 and TM090949, and the electrical data on printed page 15.

Every figure below is the pressure the unit adds on top of whatever arrives at its inlet. Pick the flow family first, then read across for the build that covers the boost you need.

CMBE 1 — to 14.5 GPM

CMBE 3 — to 26.4 GPM

Shut-off at zero flow: CMBE 3-51, 73.8 psi (170.5 ft). The 3-30, 3-62 and 3-93 curves are not drawn below 14.5, 11.7 and 4.6 GPM; at those lowest plotted points they read 38.4, 79.3 and 138.7 psi. At 4.6 to 12 GPM the 3-93 runs from 138.7 down to 123.2 psi.

CMBE 5 — to 35.2 GPM

Neither CMBE 5 curve is drawn to zero flow. The 5-31 begins at 26.4 GPM and 37.5 psi; the 5-62 begins at 20.3 GPM and 84.5 psi.

CMBE 10-54 — to 70.4 GPM

Fed by a city main — which is what CMBE is built for, since it wants a flooded suction. The drive holds the pressure you set and only makes up the difference between the main and your setting, so on a stronger main the same unit reaches that setting at a higher flow. Incoming pressure buys you more flow, not more pressure.

Drawing from an atmospheric tank — nothing arrives with pressure, so what the unit adds is what you get. Read the tables straight through, and keep the tank within 3.3 ft of the pump inlet.

Best operating range is listed per model in the ratings table above, in flow only. This is where the pump turns the most electricity into water pressure. Ask for more flow than it can deliver at your setting and it runs 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. Grundfos publishes CMBE performance only as a plotted family 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 beyond the drawn range, and nothing is transposed. Best operating ranges are derived, not published. 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), charts TM090716 (printed page 17) and TM090949 (printed page 21), ISO 9906:2012 3B. The CMBE 3-51 and CMBE 10-54 rows are read from the single-pump axis of TM090949, which draws those two curves in full.

The Grundfos GO app does not connect to the pump 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 pump by radio or infrared. Without it, the app cannot see the pump — the CMBE 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. CMBE connects to Grundfos GO through the module, so commissioning takes minutes and no laptop. Add the Grundfos MI 301 to your order.