Bore pumps get sized wrong in one of two ways: too small, so the pump can't lift water to the tank, or far too big, so it pulls the bore down and runs inefficiently. Both come from guessing. This guide shows how to work out what the bore actually needs, then match it to the 4 inch bore pumps in our Submersible & Bore Pumps range.
Step 1: get the bore numbers
Before you look at a pump, you need four facts about the bore. The driller's report usually has the first three:
- Casing size. A 4 inch pump needs a bore casing wide enough to take it. Check the pump's outside diameter on the datasheet against the casing's internal diameter.
- Pumping water level. Not the standing water level, but where the water sits once the bore is being pumped. It's always lower.
- Bore yield. How much water the bore can supply, usually in litres per minute or per hour. Never size a pump to pull more than the bore yields.
- Where the water is going. The height of the tank or house above the bore head, the pipe run, and the pressure you want at the far end.
Step 2: work out total head
Total head is the total height the pump has to push water, in metres. Add up:
- Depth from the bore head down to the pumping water level.
- Height from the bore head up to the tank inlet or highest outlet.
- Pressure you want at the outlet, converted to head. 100 kPa is about 10.2 m of head.
- Friction loss in the pipe and fittings, from the pipe maker's friction tables.
Worked example: pumping water level 30 m down, tank 8 m above the bore head, filling against atmospheric pressure, and 6 m of friction. Total head is 30 + 8 + 6 = 44 m.
Step 3: read the pump properly
Each 4BLOCK model lists a max flow and a max head. These are the two ends of the pump curve, not figures you get at the same time. At max head, flow drops to almost nothing. You need a pump whose curve gives your flow at your total head, ideally near the middle of the curve.
| Model | Motor | Max flow | Max head | Price |
|---|---|---|---|---|
| 4BLOCKm 2/12 | 0.75kW | 60 L/min | 94 m | $1,684.05 |
| 4BLOCKm 2/18 | 1.1kW | 60 L/min | 140 m | $2,129.55 |
| 4BLOCKm 4/8 | 0.75kW | 100 L/min | 63 m | $1,590.55 |
| 4BLOCKm 4/13 | 1.1kW | 100 L/min | 102 m | $2,586.05 |
| 4BLOCKm 6/10 | 1.1kW | 150 L/min | 61 m | $1,937.05 |
| 4BLOCKm 8/8 | 1.1kW | 200 L/min | 56 m | $2,283.55 |
The pattern is easy to see: for a given motor, more stages mean more head and less flow. In the 44 m example above, a 4/8 or 6/10 is in range, and the curve decides which delivers the flow you need at that head. If your total head were 80 m, only the 2/12, 2/18 and 4/13 would be candidates.
All six are 240V stainless monoblock pumps rated for clean water with sand up to 200 g/m³, liquid up to 35°C, and installation down to 100 m below water level. Each comes with 20 m of cable, so a deeper setting needs a properly jointed cable extension sized by your electrician.
Bore pump or tank submersible?
Not every submersible goes down a bore. The rest of the range is designed for tanks, wells and reservoirs:
- Hyjet HSM370-PC and HSM1100-PC ($848.05 and $1,013.05): multistage pumps with a built-in pressure controller that sit inside a rainwater tank for quiet house supply.
- Pedrollo TOP-MULTI TECH 2 ($1,838.05): built-in controller, 52 m max head, rated to 5 m submersion.
- Pedrollo NK and UP series: stainless multistage submersibles for tanks and wells. NK GE versions add a float switch for dry-run protection.
- Pedrollo TOP MULTI 1 and 2: for tanks, wells and rainwater barrels, and they drain down to 25 mm from the bottom.
A tank submersible is a good alternative to a surface pressure pump when noise matters or the tank sits below the house. For an off-grid bore, look at our solar bore pump guide.
Frequently Asked Questions
How do I work out the head for a bore pump?
Add the depth to the pumping water level, the height from the bore head to the tank or outlet, the outlet pressure as head (100 kPa is about 10.2 m), and friction loss in the pipe. That total is the head the pump has to work against.
What's the difference between max head and max flow?
They're the two ends of the pump curve. At max head the flow is close to zero, and at max flow the head is close to zero. Read the curve at your total head to see the real flow.
How deep can a Pedrollo 4BLOCK pump go?
The listings rate it for installation down to 100 m below water level. It comes with 20 m of cable, so deeper settings need a cable extension sized and jointed by an electrician.
Can a bore pump handle sand?
The 4BLOCK range is rated for clean water with sand content up to 200 g/m³. A bore producing more sand than that needs attention before you fit any pump.