Choosing a dirty water pump with a large free passage
Quick answer: the free passage is the largest particle that can pass through the pump. For lightly contaminated water, about 10 mm is sufficient; for dirty water with fibers and soft solids, 28 mm; and for coarse solids, 50 mm. Lots of fibers or wipes? Choose a vortex impeller, which rarely clogs.
What is free passage?
The free passage is the diameter of the largest solid particle that can pass through the pump unimpeded: through the suction strainer, past the impeller, and out the discharge. If a piece of debris is larger, it will get stuck and clog the pump. This is the most common cause of dirty water pumps suddenly stopping working.
How much passage do you need?
| Type of water | Free passage | Pump type |
|---|---|---|
| Clean water, rainwater | 1–3 mm | Flat suction pump or clear water pump |
| Lightly polluted: some sand, small particles | Approx. 10 mm | Drainage pump |
| Dirty water: leaves, fibers, soft solids, wipes | 28 mm | Dirty water pump (e.g., HOMA TP28) |
| Heavily polluted: coarse solids | 40–50 mm | Dirty water pump (e.g., HOMA TP48) |
| Feces with thin pressure line | N/A (grinder) | Grinder pump |
Rule of thumb: choose based on the dirtiest water you expect, not the average. One clog costs more than a pump with slightly larger passage.
Single-channel or vortex impeller?
Dirty water pumps like the HOMA TP series come in two versions:
| Single-channel impeller (M) | Vortex impeller (V) | |
|---|---|---|
| Operation | Water and debris pass through one large channel in the impeller | Recessed impeller creates a vortex; debris largely flows past the impeller |
| Head and efficiency | Higher | Lower |
| Clogging susceptibility | Low | Very low, even with fibers and stringy debris |
| Choose for | High head or long pipeline | Fibers, wipes, textiles, sludge |
Detailed explanation of all impeller types: impeller types explained.
What else to look for?
- Material: cast iron is heavy but robust and lasts a long time with daily use. For aggressive water, choose stainless steel.
- Capacity: calculate with the flow rate at your specific head, not the maximum on the box. See calculating head.
- Float: for a fixed pump sump, choose a version with a float (WA or DA).
- Voltage: 230V with plug is plug & play; 400V provides more power for heavy-duty pumps.
- Temperature: most dirty water pumps are designed for water up to approximately 40 °C.
Recommended dirty water pumps
28 MM – FIBERS AND SOFT SOLIDS
HOMA TP28 dirty water pump
Cast iron, choice of single-channel (up to 13.6 m) or vortex, 230V or 400V.
from €1,274.95
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50 MM – COARSE SOLIDS
HOMA TP48 (50 mm passage)
Up to 35 m³/hour at 14.5 m (M-version), stainless steel impeller.
from €1,465.95
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MUD AND CONSTRUCTION WATER
SPT 400R/W
Vortex impeller with agitator, bottom discharge connection.
€569.50
View pumpWastewater with feces? Then you need a lifting station.
Frequently asked questions
What is the free passage of a pump?
The diameter of the largest solid particle that can pass through the pump unimpeded. The dirtier the water, the larger the free passage must be.
What passage do I need for dirty water?
For water with leaves, fibers, and soft solids, about 28 mm. For coarse solids, 40 to 50 mm.
What is better: a vortex or single-channel impeller?
A single-channel impeller achieves a higher head. A vortex impeller is less efficient but virtually clog-free with fibers and wipes.
Why does my dirty water pump keep clogging?
Usually, the free passage is too small for the debris in the water, or wipes and fibers are getting in. Choose a larger passage or a vortex impeller.
Unsure which pump fits?
Tell us what's in the water and how high it needs to go. We'll advise you for free on the correct passage and impeller.
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