Calpeda GQN Submersible Sewage Pump

The GQN is a small submersible sewage pump on a DN50 connection, not a station pump. Calpeda puts it on civil and industrial wastewater that is not aggressive to the pump materials, on dirty water carrying solids up to 50 mm, on emptying flooded rooms and tanks, and on drawing water from ponds, streams and rainwater collection pits. The whole range is three frames on a 2-pole motor, and the pump body is common to all three.

Read the frame you are buying rather than the range. The 48 m³/h headline belongs to the 1.5 kW GQN 50-17 and arrives at 3.6 m of head, which is a transfer duty and not a lift.

Channel or vortex, and what the choice costs

Take the GQN unless the medium will bind it. Calpeda publishes both wet ends in the same coverage charts, so the cost of going the other way is not a matter of opinion.

A channel impeller is a proper hydraulic passage. What you are pumping goes through the vane, so the pump does real work on it and holds its head as flow rises. A vortex impeller sits back out of the flow and moves liquid by the swirl it creates, so very little of the medium ever touches it. That is why a vortex survives rag and filamentary material a channel would wrap, and it is also why it is a worse pump on the curve.

The GQV is the vortex build of the same family. Same 2-pole motor, same 50 mm free passage on the DN50 frames, same cast iron impeller material, same double seal. Only the wet end changes. At 50 Hz, Calpeda's coverage charts put the two side by side:

The gap widens as you move right along the curve. At 1.1 kW and 36 m³/h the channel build gives 5 m and the vortex gives 2 m. Push further and the vortex is simply not there: the GQN 50-15 is still on its curve at 42 m³/h, where the GQV 50-13 has run out at 36 m³/h.

Put that in terms of what you pay. Suppose the duty is 24 m³/h at 8 m. The 1.1 kW GQN 50-15 sits on it at 8.3 m and draws 3.3 A at 400 V. The 1.1 kW vortex cannot reach it, because a GQV 50-13 gives 6.7 m there, so you go up a frame to the 1.5 kW GQV 50-15, which gives 8.5 m and draws 4 A. That is a bigger motor and more current for the same water moved to the same place, for as long as the pump is in the chamber.

So the vortex has to earn that, and Calpeda says plainly where it does. The instructions covering the GQ, GX and GM ranges direct you to the free-flow vortex or grinder builds where the liquid has a high solid content or carries filamentous particles. The GQN is not on that list. Both pumps pass a 50 mm sphere, so free passage is not what separates them. What separates them is what happens to a length of fibre once it is inside.

Neither is a macerator. Where a chamber is putting through more wipes than any impeller was going to clear, the fix is screening or maceration upstream, not a different impeller and not a bigger pump.

Where the GQN stops

The GQN takes liquid to 35°C and no hotter, at pH 6 to 11 and a density up to 1100 kg/m³. Maximum immersion is 5 m, minimum immersion is 275 mm, and the motor is rated for continuous duty only while it is submerged. Maximum permissible working pressure in the pump body is 25 m, which is 2.5 bar.

The starts limit is the one that catches people out on small chambers. Calpeda allows 30 starts an hour at regular intervals. A wet well sized on flow alone, with no thought to the drawdown volume between the float levels, will exceed that and cook the motor long before anything hydraulic goes wrong.

The published heads assume a medium behaving as water: density 1.0 kg/dm³ and kinematic viscosity no greater than 20 mm²/s. Thicken the medium beyond that and the curve you selected against is no longer the curve you have.

The GQN draws through a 50 mm free passage in the base, works the medium with a cast iron channel impeller, and discharges vertically through a G 2 threaded port to ISO 228. Calpeda calls the arrangement a patented system. The motor is a 2-pole submersible induction motor running at about 2900 rpm at 50 Hz, and the whole unit is IP X8 for continuous immersion.

The motor and the winding

The winding is a dry type with triple moisture-resistant impregnation, class F insulation, built to EN 60034-1, EN 60335-1 and EN 60335-2-41. Sound pressure is under 70 dB(A) at minimum immersion depth, and the noise falls away as the pump submerges. On request Calpeda will supply other voltages, 60 Hz, a 20 m cable, a motor set up to run on a frequency converter, and a three-phase pump with an integral float switch.

Two seals and an oil chamber

The shaft runs through two mechanical seals with an oil chamber between them. Both faces are ceramic against carbon with NBR elastomers, and the chamber is filled with an oil for food and pharmaceutical machinery.

Two seals in series is not the same as one seal and a lip. Wear the pump-side face and the oil chamber is still standing between the sewage and the windings. The weak point in almost any pump is the seal, and dry running is what takes it out fastest: a mechanical seal needs liquid to lubricate it, and the faces go as soon as the film does. On a submersible that usually means a float that has stopped swinging, or a chamber drawn down below the 275 mm minimum immersion.

The electrical side

Three-phase GQN runs on 230 V or 400 V ±10%, drawing 2.3 A, 3.3 A and 4.5 A at 400 V across the 0.9, 1.1 and 1.5 kW frames. It ships with 10 m of H07RN-F 4G1 mm² cable and no plug, so the overload protection comes from your starter or your board.

Single-phase GQNM runs on 230 V ±10% with a built-in capacitor, a thermal protector and a float switch fitted as standard, on 10 m of H07RN-F 3G1 mm² cable with a CEI-UNEL 47166 plug. Full load current is 6.6 A, 8.4 A and 12 A across the three frames, with 25, 30 and 35 µF capacitors rated at 450 V. Note the input power against the output: the 1.5 kW GQNM 50-17 draws 2.2 kW at the input.

Reading the designation

GQ is the series and N is the channel impeller. An M after that means single-phase, and no letter means three-phase. Then 50 is the free passage in millimetres, and 13, 15 or 17 is the nominal total head in metres. So a GQNM 50-15 is the single-phase 1.1 kW pump with a 50 mm passage. If you are matching an existing unit, photograph the nameplate and send us the full designation and the serial number.

Where it must not go

Calpeda's instructions are explicit that the pump must not be installed in a potentially explosive atmosphere, and must not be used in ponds, tanks or swimming pools while people are in the water. If your chamber is a classified hazardous area, this is not the pump, and the answer is a certified unit rather than a risk assessment written around this one.