When wastewater has to be pumped rather than drained by gravity, there are three types of pump that get mentioned, and they are often treated as interchangeable. They are not. A sewage pump, a cutter pump and a grinder pump deal with solids in very different ways, and choosing the wrong one leads either to blockages or to spending far more than the job needs. The right choice comes down to one question: what is in the water, and how does the pump need to deal with it.
Sewage pump: passes solids whole
A standard sewage pump is designed to pass soft solids through the pump without cutting them up.
It does this with a large impeller and a wide internal passage, often a vortex impeller that creates a swirling flow so solids travel through with minimal contact. The key specification is the free passage, the diameter of the largest solid the pump can pass, which on a typical sewage pump is around 50mm so it can handle the soft solids found in domestic foul water. The APP BCV vortex sewage pump and the EVAK Hippo are good examples, and you will find the range in our sewage pumps collection.
This is the right pump for most domestic and light commercial foul drainage where the discharge pipe is a sensible diameter and the system handles normal waste. It is the simplest and most economical of the three, and where it suits the job there is no reason to pay for a cutter or grinder.
Cutter pump: slices solids as they pass
A cutter pump adds a hardened cutting edge at the intake that slices stringy and fibrous material as it enters, before it can wrap around the impeller and block it. It does not turn waste to slurry, it chops it into smaller pieces so they pass through more easily. This matters where the waste includes the things that defeat a plain sewage pump, above all wet wipes, rags and fibrous matter, which knit together and cause the blockages that sewage pumps are blamed for. An example is the APP DSPK which is a popular sewage cutter pump.
A cutter pump is the sensible step up where a system sees difficult waste, or where the discharge pipe is narrower than a plain sewage pump would need. It buys reliability in exactly the situations that cause call-outs.
Grinder pump: macerates to a slurry and pumps far
A grinder pump goes further again. It macerates solids into a fine slurry using a grinding mechanism, then pumps that slurry at high pressure through a small-bore pipe, sometimes only 32mm or 40mm. The grinding produces a fluid that behaves almost like water, and the pump is built for pressure rather than free passage.
An example of this is the Speroni Cutty Grinder Sewage Pump. The Cutty is manufactured by Speroni Pumps. What makes a grinder pump different from a standard sewage pump is the cutting mechanism at the inlet: rotating blades shred solids, fibres, and waste into a pulp before the pump moves it. That pulp can then be pumped through small-bore pipe, sometimes over long distances, without blocking.
Grinder pumps are the specialist, higher-cost option. You choose one when the situation demands long-distance or uphill pumping through a small pipe, not simply because it sounds like the most capable. For most foul drainage it is more pump than the job needs.
How to choose
One more point that sits alongside the pump choice:
One more point that sits alongside the pump choice: foul water pumping is covered by Building Regulations, and the installation has to meet them. We cover that in our guide to sewage pumps and Building Regulations, and if you are weighing up whether you even need a foul pump or a surface water one, our sewage pump vs sump pump guide clears that up. For a complete buried system, see our packaged pump stations.
Frequently asked questions
What is the difference between a sewage pump and a grinder pump?
A sewage pump passes soft solids through whole using a wide passage and often a vortex impeller. A grinder pump macerates solids into a fine slurry and pumps it at high pressure through a small-bore pipe. The sewage pump suits normal gravity-fed foul drainage; the grinder pump suits pressurised systems that push waste a long way or uphill.
Do I need a cutter pump for wet wipes?
If a system regularly sees wet wipes, rags or other fibrous material, a cutter pump is the safer choice. It slices that material as it enters, before it can wrap around the impeller and cause the blockage that a plain sewage pump is prone to with this kind of waste.
Can I use a grinder pump for everything to be safe?
You can, but it is usually more pump than the job needs and costs more to buy and run. A grinder pump earns its place where waste must be pumped through a small-bore pressure pipe over distance or uphill. For normal foul drainage a standard sewage pump is the right and cheaper answer.
What size solids can a standard sewage pump handle?
A typical domestic sewage pump has a free passage of around 50mm, meaning it can pass soft solids up to that diameter. The free passage figure on the pump specification tells you the largest solid it will pass, which is the number to check against your system.
