Calpeda GQS Submersible Sewage Pump, Free-Flow Vortex

The GQS is a small submersible sewage pump built around one idea: a free-flow vortex impeller. Calpeda puts it on civil and industrial wastewater that is not aggressive to the pump materials, on dirty water carrying solids of 40 or 50 mm, on emptying flooded rooms and tanks, and on drawing water out of ponds, streams and rainwater pits. It is 2-pole, it goes in the chamber on a vertical G 1½ or G 2 port, and it is cast iron where the sewage touches it and stainless everywhere else.

One line of the published headline needs correcting before you size anything. Calpeda's product page gives the power range as 0.55 to 2 kW. That range covers the GQS and the GQV together, and it misses the bottom of the GQS: the smallest row in the 50 Hz tables is the 0.45 kW GQS 40-9. Read the frame you are buying off the datasheet, not the range off the product page.

The free-flow vortex impeller, and when Calpeda says to use it

Buy the GQS when the flow carries rag, wipes or fibre. That is the verdict, and Calpeda's own instruction manual is unusually direct about it: where the liquid has a high solid content or filamentous particles, use only the free-flow construction or a grinder.

The mechanism is worth a paragraph, because it explains the cost as well as the benefit. A free-flow vortex impeller sits back out of the flow path and moves the liquid by the swirl it creates, so very little of what you are pumping ever touches it. A length of fibre travels through the casing on the swirl and mostly never meets a vane. That is what keeps the pump running on a duty that would bind a channel impeller, and it is also what makes it a less efficient pump. You pay for it in power, every hour it runs. Where the medium is seepage, grey water or a clean excavation, a channel impeller such as the GQN holds a better duty point on the same motor, and that is the pump to take.

Calpeda's 50 Hz tables give you the six GQS frames:

Read across a duty rather than down the headline. Say you need 18 m³/h at 7 m. The 0.9 kW GQS 50-11 gives exactly 7 m there, which is no margin at all, so you take the 1.1 kW GQS 50-13 and its 8.6 m. The 0.75 kW GQS 50-9 manages 5.3 m at that flow and is not in the running.

The 40 frame is worth a second look on a tight duty. At 0.45 kW the GQS 40-9 starts at 9.3 m, higher than the 0.55 kW GQS 50-8 at 8 m. It buys that head by passing 40 mm instead of 50 mm and running out of curve at 21 m³/h. If the solids are small and the head is what hurts, it is the cheaper pump to run.

GQS or GQV: the same impeller, a different delivery

The impeller is not the difference. Calpeda's designation key gives S and V the same meaning, a free-flow vortex impeller, and describes both ranges in one sentence as single-impeller submersible pumps with a free-flow (vortex) impeller. What separates them is how the pump connects and how it is installed.

The GQS takes a vertical threaded port, G 1½ on the 40 frame and G 2 on the 50 frames. The GQV takes a horizontal port, threaded or flanged, and Calpeda's manual lists the GQV among the pumps installed on automatic coupling feet and guide rails. The GQS is not on that list. So the GQS is the pump you drop into a chamber on a hose or a screwed pipe, and the GQV is the one you set up to lift off a duckfoot bend without anybody entering the wet well. The GQV also extends the range upwards to a 65 mm free passage, which the GQS does not reach.

If your station has guide rails, that decides it before any curve does.

The GQS 40 is a different pump from the GQS 50

Calpeda changes the build on the 40 frame, and the materials list is where you see it. The impeller is 1.4301 (AISI 304) stainless rather than cast iron, the shaft is 1.4305 (AISI 303) rather than 1.4301, the winding gets double impregnation rather than triple, and the materials table lists no upper mechanical seal on this frame. Minimum immersion is 200 mm against 275 mm on the 50 frames, which on a shallow sump can be the whole argument.

When you are matching an existing installation, read the frame off the nameplate and treat it on its own terms.

Where the GQS stops

The limits come off the datasheet and the manual, and most of them are set by the sump rather than the pump. Liquid temperature stops at 35°C, and a single-phase motor run for long above that will stop on its thermal protector and restart when the windings have cooled. The medium must sit between pH 6 and pH 11. Maximum liquid density is 1100 kg/m³. Maximum immersion is 5 m. Starts are limited to 30 an hour at regular intervals, which on a small chamber is a wet-volume calculation as much as a pump selection. Maximum permissible working pressure in the casing is 25 m (2.5 bar), which the range's own 15 m of head never approaches.

Calpeda states plainly that the pump cannot be used in explosive or flammable environments, and that it must not be used in garden ponds, tanks or swimming pools while people are in the water.

The GQS draws sewage in through the base of the pump, works it with a free-flow vortex impeller in cast iron, and discharges up through a vertical G 1½ or G 2 ISO 228 port. The motor is a 2-pole induction motor running at about 2900 rpm at 50 Hz, rated for continuous duty with the motor submerged, IP X8 for continuous immersion and insulation class F, with a humidity-proof dry winding. Calpeda builds it to EN 60034-1, EN 60335-1 and EN 60335-2-41. The tabulated head and power figures hold for a liquid at density 1.0 kg/dm³ and a kinematic viscosity no higher than 20 cSt, so a thicker or heavier medium moves the duty point off the published curve.

What the recessed impeller actually does

The GQS impeller is set back in the casing, and the pumping is done by the vortex it spins up in the space in front of it. Solids ride that swirl out of the discharge rather than passing through a vane. Compare that with a channel impeller, where the liquid goes through a vane passage and a length of fibre that catches on a leading edge stays there and collects more. The free passage, 40 mm or 50 mm depending on the frame, is the size of solid that fits through the casing, not a promise about what the vane will tolerate, because on this build very little reaches the vane at all.

Two seals and an oil chamber

The shaft runs through a double mechanical shaft seal with an oil chamber between the faces. Upper and lower seals are both ceramic against carbon with NBR elastomers, and the chamber holds oil for food and pharmaceutical machinery. Calpeda's stated purpose for the arrangement is protection against dry running.

Dry running is still what kills it fastest. A mechanical seal needs liquid to lubricate it, and the faces go as soon as the film does. Calpeda's instruction is short: avoid running dry, and on a build without a float, start the pump only when it is fully immersed. On a sewage chamber that usually means a level control that has stopped working, or somebody drawing the sump down further than the design allowed. The manual also warns against taking the pump out of the water while it is still running, and notes there may be slight pressure in the oil chamber when you open the plug.

The air release valve

The GQS is fitted with a relief valve that lets air out from around the impeller, so the pump primes properly after a long standstill. On an intermittent duty that is the part worth knowing about, because it is the part that stops working quietly. Calpeda asks you to check periodically that the relief valve (item 14.80) has not clogged with impurities.

The electrical side

Single-phase GQSM builds run on 230 V ±10% with an incorporated capacitor, a thermal protector, a float switch and a CEI-UNEL 47166 plug, on 10 m of H07RN-F 3G1 mm² cable. Capacitors run 16 to 35 µF at 450 V. Full load current is 4.3 A to 13 A across the frames. Maximum power input P1 runs from 0.95 kW to 2.2 kW, so size the supply against P1 rather than the rated output.

Three-phase GQS builds run on 230 V or 400 V ±10% on 10 m of H07RN-F 4G1 mm² with no plug, drawing 1.5 A to 4 A at 400 V. Calpeda's manual is explicit that you install the overload-protective device in the control box, with a curve D characteristic set to the nameplate current, and that where the water level is not under direct visible control you add a float switch wired to the panel to set the start and stop levels. Check the direction of rotation at first start. Running backwards costs you delivery, causes vibration and can damage the mechanical seal.

Other voltages, a 60 Hz build, a different mechanical seal, a 20 m cable, a motor set up for inverter duty and a three-phase pump with a built-in switch and float are all listed by Calpeda as available on request.

Installing and servicing it

Keep the internal diameter of the delivery pipe at or above the port size, and fit a check valve in the delivery against back flow. Arrange a gate valve and a union so the pump can come out without draining the system. Where slime collects at the bottom of the pit, stand the pump on a support so it sits clear. Sand and grit are what wear a submersible out, so in stagnant water or a river intake mount it on a flat surface raised off the ground. Use a rope or chain to lower and lift it, never the power cable, and leave a little slack in the cable so the delivery pipe expanding under load does not strain it.

To inspect the impeller, take out the screws (14.24) and the pump casing (14.00), and check the impeller turns freely by hand. The impeller comes off with the nut (28.04). After pumping muddy liquids, run the pump briefly on clean water before it stands idle. If there is a risk of freezing, take it out of the water and leave it somewhere dry.

Reading the designation

Calpeda's key runs GQ for the series, then the impeller letter, then M for single phase, then the free passage, then the head. S is the vertical free-flow vortex build and V the horizontal one, and no M means three phase. The number after the letters is the free passage diameter in millimetres, and the number after the dash is Calpeda's total head figure, which lines up with the head at zero flow in the tables. So a GQSM 40-9 is a single-phase free-flow pump with a 40 mm passage and about 9 m of head, and a GQS 50-15 is the three-phase 1.5 kW frame with a 50 mm passage. If you are matching an existing unit, read the full designation and the serial number off the nameplate and send us both.