Calpeda GX 40 Stainless Steel Submersible Drainage Pump

The GX 40 is the stainless drainage and sewage end of Calpeda's submersible range. It is a single-impeller pump in chrome-nickel stainless steel with a vertical delivery port, and Calpeda puts it on clean and dirty water carrying solids up to 35 mm grain size. It is 2-pole, 0.55 kW to 0.9 kW, on a G 1½ (DN 40) connection, and it goes in the sump on the end of a hose or a screwed pipe rather than onto guide rails.

Size it against the 50 Hz datasheet, not against a summary range. The tables are where the frames are. There are three rated outputs, 0.55, 0.75 and 0.9 kW, and the widest curve in the range stops at 26 m³/h and 12.9 m, both on the GXC 40-13.

Calpeda also notes that the smooth rolled-stainless surfaces and the easy access for cleaning make this construction suitable for certain uses in the food industry. That is Calpeda's wording about the build, and on a wash-down floor it is worth having. Where the duty needs a certificate behind it, send us the specification and we will put it to Calpeda.

Two-passage or vortex, and what the vortex costs

Take the GXC 40 unless the medium will bind it. Here is what each side costs you.

A two-passage impeller is a proper hydraulic passage. The liquid goes through the vanes, so the pump converts the motor's work efficiently and holds a real duty point. A free-flow vortex works the other way round. The impeller is recessed up into the casing and drives the water by the swirl it sets up, so most of what you pump never reaches the vanes. That is why it takes rag and fibre a vane would catch, and it is also why it gives up so much duty.

Calpeda's own 50 Hz tables price it:

Read the 0.9 kW pair. At 12 m³/h the GXC 40-13 gives 8.7 m and the GXV 40-9 gives 5.4 m, for the same motor and the same 35 mm passage. At 21 m³/h the GXC is still holding 5.9 m while the vortex has fallen to 2.4 m and stopped. Suppose the duty is 15 m³/h at 7 m. The 0.9 kW GXC 40-13 sits on it with 7.8 m to spare at that flow. No GXV 40 in the range reaches it, because the biggest vortex build gives 4.5 m there. On the GX 40 the vortex does not cost you a frame size, it costs you the duty.

So the vortex has to earn that, and Calpeda's instruction manual says when it does: where the liquid has a high solid content or carries filamentous particles, use only the free-flow construction. Wipes, rag and fibre are that case. A two-passage impeller that blocks costs a lifted pump and a site visit every time, and that arithmetic beats a few metres of head quickly. Seepage, a flooded basement, a clean excavation or a rainwater sump is not that case, and the GXC is the right answer and the better pump on the duty.

Neither is a macerator. Where a chamber is putting through more rag than any impeller was going to clear, the fix is screening or maceration upstream, not a different wet end. The enquiry we decline most often is a like-for-like swap on a pump that keeps clogging when the pump already fitted was a good solids-handling pump.

Reading the designation, and one trap in it

Calpeda's key runs GX for the series, then the impeller letter, then M for single phase, then the port size, then the head. C is the two-passage impeller, V the free-flow vortex, and no M means three phase. So a GXCM 40-10 is a single-phase two-passage pump on a 40 mm port, and a GXV 40-9 is a three-phase vortex. The last number is Calpeda's total head figure in metres, and it lines up with the head at zero flow in the tables.

The trap is the middle number. On this range the 40 is the delivery port diameter in millimetres. On Calpeda's smaller stainless submersibles the same position carries the solids passage instead, so a GXV 25 is a 25 mm passage, not a 25 mm port, and it is a different, lighter pump on a G 1¼ connection. Two pumps in the catalogue wear a V and a two-digit number and they do not mean the same thing. If you are matching an existing unit, read the full designation and the serial number off the nameplate and send us both.

Where the GX 40 stops

The limits are set by the sump, not the pump. Liquid temperature stops at 35°C, and a single-phase motor run for long in water above that will trip its thermal protector and restart when the windings cool. Maximum immersion is 5 m. Maximum liquid density is 1100 kg/m³. Starts are limited to 30 an hour at regular intervals, which on a small chamber is a volume calculation as much as a pump selection. Calpeda's manual also puts a ceiling of 25 m (2.5 bar) on the working pressure in the casing, which the range's own 12.9 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 ponds, tanks or pools where people are in the water.

The GX 40 draws through the base of the pump, works the liquid with either a two-passage or a free-flow vortex impeller in 1.4301 stainless, and discharges up through a G 1½ 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 and insulation class F, with a triple-impregnation humidity-proof dry winding. Calpeda builds it to EN 60034-1, EN 60335-1 and EN 60335-2-41. The head and power figures in the tables hold for a liquid at density 1.0 kg/dm³ and a kinematic viscosity no higher than 20 cSt.

The two wet ends

Both builds pass 35 mm spherical solids, so free passage is not what separates them. What separates them is what happens to a length of fibre once it is inside. In the GXC it has to travel down a vane passage, and if it catches on a leading edge it stays there and collects more until the passage shuts. In the GXV it is carried round the open casing and out, because there is no vane in its path to catch on. You pay for that in efficiency, every hour the pump runs.

Two seals and an oil chamber

The shaft runs through a double shaft seal with an oil chamber between the two faces. Both the upper and the lower mechanical seal are ceramic against carbon with NBR elastomers, and the chamber holds 0.08 litres of white oil suitable for food machinery and pharmaceutical use. Wear the lower face and the oil chamber is still between the liquid and the windings.

Dry running is what kills the arrangement fastest. A mechanical seal needs liquid to lubricate it, and the faces go as soon as the film does. Calpeda's instruction is short on this: avoid running dry, and on a build without a float, start the pump only when it is fully immersed. On a drainage pump that usually means a level control that has stopped working, or somebody pulling the sump down further than the design allowed. Calpeda's manual also warns against taking the pump out of the water while it is still running.

The electrical side

Single-phase GXCM and GXVM builds run on 230 V ±10% with an incorporated capacitor, a thermal protector, a float switch and a plug, on 10 m of H07RN-F 3G1 mm² cable. Full load current is 4.6 A on both 0.55 kW builds, 5.4 A on the 0.75 kW GXVM 40-8, 6 A on the GXVM 40-9 and 6.6 A on the GXCM 40-13. Maximum power input runs from 1 kW to 1.45 kW, so size the supply against P1 rather than the rated 0.9 kW output.

Three-phase GXC and GXV builds run on 230 V or 400 V ±10% and come with cable and no plug. Calpeda's manual is explicit that you fit 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. Full load current at 400 V is 1.6 A on the GXC 40-10 and the GXV 40-7, 2.2 A on the GXV 40-8 and 2.3 A on the GXV 40-9 and the GXC 40-13. Check the direction of rotation on first start; running backwards costs you delivery and can damage the mechanical seal.

A float switch on the three-phase build, other voltages, a 60 Hz build, a 20 m cable, a different mechanical seal and a motor suitable for inverter duty are all listed by Calpeda as available on request.

Installing and servicing it

Keep the internal diameter of the delivery pipe at G 1½ (DN 40) or larger, fit a check valve in the delivery against back flow, and arrange a gate valve and 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 stainless drainage pump out, so on 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.

To look at the impeller on a GXC or GXV, take out the nuts (12.20) and lift off the casing cover (12.00), then check the impeller turns freely by hand. The impeller itself comes off with the nut (28.04). After pumping muddy liquid, run the pump briefly on clean water before it stands idle. The oil chamber can be under slight pressure, so open the plug carefully.