Product group 03
The installation's only moving part that carries energy. A wrongly selected pump neither falls short nor delivers too much — it just keeps running at the wrong point and inflates the bill.
In-line centrifugal pump · volute casing with coupled motor
Why it matters
The pump alone generates the majority of the installation's operating cost. A pump running at the right point is both quiet and long-lived.
A pump doesn't offer a single flow rate or a single pressure — it offers a curve. Its real operating point is where that curve intersects the installation's resistance curve. A pump selected by glancing at a catalog usually misses that point.
An oversized pump gets throttled by a valve, converting the pressure it generates straight into wasted heat. Operating in the zone where the efficiency curve peaks makes a double-digit difference in annual consumption.
Heating and cooling load isn't constant throughout the day. A speed-controlled pump slows down to match demand; since consumption drops with the cube of speed, savings turn out larger than expected.
If there isn't enough pressure at the suction, the fluid vaporizes at the impeller inlet, and the collapsing bubbles erode the impeller. A pump selected without an NPSH calculation reveals itself within months through noise and vibration.
On critical lines, two smaller pumps are safer than one large one. If one fails, the system keeps running, even if at reduced capacity; the line doesn't stop during maintenance.
A mechanical seal is a wear part; its life varies with the fluid and temperature. With the right type selected, the maintenance interval becomes predictable and the risk of a sudden shutdown drops.
Types
Body type determines the mounting style, and mounting style determines ease of maintenance.
Sits directly on the pipeline, needs no separate foundation. The standard solution for heating and fan coil circuits.
Coupled to a base via a coupling. For lines requiring high flow rate and head.
Produces high pressure through stages in series. For building potable water pressurization and high-rise structures.
Selection criteria
Selection can't be made without the first two items. The rest determine the model and equipment.
Flow rate
The amount of fluid that must pass through the line. Calculated from capacity and temperature difference for heating, from consumption for potable water.
m³/h or l/s
Head
The installation's total resistance: pipe friction, fitting losses, and any elevation difference. If underestimated, the flow rate won't hold.
mWC or kPa
Fluid type and temperature
Water, a glycol mix, or a process liquid. Glycol increases viscosity; more power is needed for the same flow rate.
Fluid + °C + % ratio
Suction conditions and NPSH
Suction elevation, liquid level and suction-line resistance. This is the one calculation that determines cavitation risk.
NPSHa value
Operating regime
Constant flow or variable? For a variable load, the variable frequency drive selection needs to be made from the start.
Constant / variable
Redundancy requirement
A single pump, a duty-standby pair, or a parallel group? Downtime tolerance is decisive on critical lines.
1+0 / 1+1 / parallel
Motor efficiency class and supply
IE3 is the minimum standard; IE5 offers higher efficiency. Voltage and phase information must be confirmed.
IE class + 230/400 V
Connection size and mounting location
Flange size, shaft height and service clearance. Maintenance clearance in tight boiler rooms is often overlooked.
DN size + mounting clearance
You don't need all of it. We'll work out anything missing together with you.
Create a quote requestFAQ
The four questions we hear most often at the quote stage.
We can, but it's often not the best choice. The old pump was either wrongly selected from the start, or the installation has changed since then. We can source the same model from the nameplate data; we'll also run a quick check to tell you whether it's actually running at the right point.
Not every sound means a fault. A gravel-like sound from the suction side points to cavitation, a continuous hum points to bearing wear, and vibration in the line points to the wrong operating point. The character of the sound and where it's heard narrow the diagnosis considerably; we can talk through it together.
No. On lines where the load is constant, the added cost doesn't pay back. In variable-flow systems, fan coil circuits and pressurization groups, the payback period is usually short. If we know the load profile, we can tell you which makes sense.
A strainer on the suction side, a check valve on the discharge, isolation valves on both sides, and a vibration-absorbing compensator. A pressure gauge and, if needed, a balancing valve belong in the same group. Bundling these into a single quote is an advantage for both installation and lead time.
Next step
Share the flow rate and head, and let's work out the right model on the curve.