Rising Main Friction Loss: Choosing Pumps for Long Sewer Mains
On a long sewer rising main, pipe friction usually becomes the largest part of the pump's duty head, so the pipe diameter and the pump have to be selected together. Pick the pipe first so the velocity sits between about 0.7 and 2 m/s, calculate the friction loss at peak flow, add the static lift and residual head, and only then choose a pump whose curve passes through that duty point with margin.
Most pump selection mistakes on long mains come from the reverse order: choosing a pump, then discovering the main it has to push through. This guide works a 400 metre example with real numbers and shows why one pipe size up can halve the pump cost. It is written for hydraulic consultants, builders and plumbing and civil contractors.
Got a long main on the drawings? Our commercial pump station service checks the rising main, selects the pumps and controller and returns a supply quote, usually within 24 to 48 hours. Grinder pumps for small bore pressure mains start with the Aline SABRE ALG1500-1 at $2,215.39.
Why rising main length changes pump selection
Rising main length changes pump selection because friction loss grows in direct proportion to length, so on a main of a few hundred metres friction can exceed the static lift several times over.
On a short main, total head is mostly static lift: the height from the pump's stop level to the discharge point. On a long main, the static lift may be 8 metres and the friction 20 metres. A pump chosen on static lift alone will run, push almost nothing, and the high level alarm will tell you about it on the first wet afternoon.
Total duty head for a sewer rising main is:
- Static lift: from the pump off level in the wet well to the highest point of the main or the discharge invert, whichever is higher.
- Pipe friction: calculated at the design flow over the full length of the main.
- Minor losses: bends, valves and fittings. On long mains these are small relative to pipe friction; an allowance of about 10% of pipe friction is a common starting point.
- Residual head: a margin at the discharge, typically 1 to 2 metres into a gravity manhole, more if discharging into a pressurised system.
How to calculate rising main friction loss
Rising main friction loss is commonly calculated with the Hazen Williams formula, which gives head loss from flow, internal diameter, length and a roughness coefficient C.
In SI units: head loss (m) = 10.67 multiplied by length (m) multiplied by Q1.852, divided by C1.852 multiplied by D4.87, with Q in m³/s and D the internal diameter in metres.
Three things matter in practice:
- Use the internal diameter, not the nominal size. A DN63 PE100 SDR11 pipe has an internal diameter of about 51.4mm, not 63mm. Using the outside diameter understates friction badly, because loss scales with D to the power 4.87.
- Pick a realistic C value. New PE is often quoted at C = 150. A sewer main ages and slimes up, so a value around 140 is a more conservative design figure. The examples below use 140.
- Calculate at peak flow. The pump must clear the peak inflow, and friction at peak is the number that sets the duty point.
Worked example: 400 metre sewer rising main
For a 400 metre rising main carrying 1.5 L/s (90 L/min) with 8 metres of static lift, DN63 PE gives the best balance: 0.72 m/s velocity and about 15.5 metres of total duty head.
The site: a small commercial building discharging to a gravity sewer manhole 400 metres away. Peak design flow 1.5 L/s, static lift 8 metres, residual 2 metres, PE100 SDR11 pipe, C = 140, minor losses at 10% of pipe friction.
| Pipe (PE100 SDR11) | Internal diameter | Velocity at 1.5 L/s | Pipe friction, 400 m | Total duty head | Verdict |
|---|---|---|---|---|---|
| DN40 | 32.6 mm | 1.80 m/s | 46 m | About 61 m | Unworkable with packaged sewage pumps |
| DN50 | 40.8 mm | 1.15 m/s | 15.6 m | About 27 m | Possible, but pushes pumps near their maximum head |
| DN63 | 51.4 mm | 0.72 m/s | 5.0 m | About 15.5 m | Best balance |
| DN75 | 61.4 mm | 0.51 m/s | 2.1 m | About 12.3 m | Too slow, solids will settle |
Calculated with Hazen Williams, C = 140. Internal diameters are typical for PE100 SDR11; check the manufacturer's figure for the pipe class actually specified.
Look at the jump from DN50 to DN63. One size up cuts the duty head from about 27 metres to about 15.5 metres. That is the difference between a pump working near its limit and a pump working in the middle of its curve.
Choosing the pump for the duty point
The right pump for a long rising main is one whose published curve passes through the duty point with margin, not one whose maximum head merely exceeds it.
Maximum head is the head at zero flow. A pump rated to 30 metres maximum delivers nothing at 30 metres. On the worked example above, here is how the live range lines up:
| Pump | Type and supply | Max head | Max flow | Price | Fit for 90 L/min at 15.5 m (DN63) |
|---|---|---|---|---|---|
| Aline SABRE ALC750-1 | Cutter, 0.75kW, 240V | 14 m | 450 L/min | $1,433.75 | No. Duty head exceeds maximum head |
| Aline SABRE ALG1500-1 | Grinder, 1.5kW, 240V | 30 m | 240 L/min | $2,215.39 | Candidate. Confirm on the curve |
| Aline SABRE ALG1500-3 | Grinder, 1.5kW, 415V | 30 m | 240 L/min | $2,131.97 | Candidate where three phase is available |
| Aline SABRE ALG2200-3 | Grinder, 2.2kW, 415V | 28 m | 240 L/min | $2,551.43 | Candidate. Confirm on the curve |
| Aline SABRE ALG3700-3 | Grinder, 3.7kW, 415V | 34 m | 360 L/min | $5,060.35 | Oversized here. Considered for the DN50 option |
Prices current as of November 2026, AUD including GST, per pump. Maximum head and flow from each product page.
The cutter pump drops out immediately. Cutter pumps move high flow at low head, which suits short mains, not this one. The 1.5kW grinders are the logical candidates on DN63. Stay on DN50 and the 27 metre duty pushes the selection towards the ALG3700-3: more than double the pump cost per unit, doubled again in a duty and standby station, and a higher running cost for the life of the building. The bigger pipe is almost always cheaper than the bigger pump.
View the Aline SABRE ALG1500-1 grinder pump →
Velocity limits on a sewer rising main
A sewer rising main should run at roughly 0.7 to 0.8 m/s or more at design flow so solids stay in suspension, and generally below about 2 to 2.5 m/s to limit friction and surge.
The lower limit is the one that gets missed. Upsizing the pipe to cut friction is good practice until velocity drops below self cleansing. In the example, DN75 halves the friction again but runs at 0.51 m/s, and solids will settle in the low sections between pump cycles. Grinder pumps help, because ground solids stay in suspension more easily, but they do not make a slow main self cleansing. Check the specific water authority or project specification, because minimum velocity requirements vary.
Retention time and odour on long rising mains
Long rising mains hold sewage between pump cycles, and sewage that sits for hours turns septic, generating hydrogen sulphide that causes odour and corrodes concrete at the discharge manhole.
The 400 metre DN63 main in the example holds about 830 litres. If each pump cycle moves around 135 litres, it takes about six cycles to push a slug of sewage from the station to the manhole. At night, on a commercial building with almost no inflow, that can be many hours. Practical responses:
- Keep the main as small as the velocity and head allow, so it holds less volume.
- Size the active volume in the wet well so each cycle moves a meaningful share of the main.
- Raise odour and corrosion at the discharge manhole with the designer and the water authority early. Ventilation, odour control or a lined receiving manhole may be required.
Air valves, scours and surge
A long rising main with high points needs air release valves at those high points, and low points may need scour valves for draining and maintenance.
Trapped air at a high point acts like an added restriction and can push the real duty head well above the calculated figure. Surge also deserves a check on long mains: when a pump stops, the moving column of water decelerates and the check valve slams. Longer mains and higher velocities make it worse, which is another reason not to run the pipe too small. Where the profile undulates or the main is very long, a hydraulic designer should check surge and valve placement.
Two pumps on one long rising main
Two pumps running together on a long rising main deliver far less than double the flow, because friction rises with roughly the square of flow and dominates the system curve.
On the DN63 example, doubling flow to 3 L/s raises pipe friction from about 5 metres to about 18 metres, and the duty head to about 30 metres. A pair of 1.5kW grinders will not get there together. So on long mains, specify duty and standby with each pump meeting the peak duty alone, and treat assist as a bonus. Our dual pump controller guide covers how the controller handles alternation, standby changeover and assist.
Packaged stations for long rising mains
A packaged dual station with grinder pumps is the usual answer for a commercial site on a long small bore rising main, because the tank, pumps, controller and pipework arrive matched.
The Kwikflo Dual Sewer Pump Station (from $5,716.28) comes in 900L, 1,200L or 2,000L poly with a cutter or grinder pump option, which lets the pump suit the main. The BlueSelect 700L Dual Pump Station (from $7,873.93) ships with grinder pumps, automatic changeover and guide rail lift out kits. For stations under driveways or car parks, add a trafficable Class D pit lid.
For the whole station design, including inflow, storage and the system curve, read the commercial sewer pump station sizing guide. Typical applications are on the commercial building sewer pump stations and mine site sewer pump stations pages, and the full range is in packaged pump stations and submersible sewage pumps. Longer mains and bigger duties beyond the listed range are supplied as custom packages on quote.
Frequently asked questions
What is a rising main in a sewer system?
A rising main is the pressurised pipe that carries sewage from a pump station up to a higher discharge point, usually a gravity sewer manhole. Unlike a gravity sewer, it runs full and under pressure, so the pump has to overcome static lift plus friction along its length.
How do you calculate friction loss in a rising main?
Friction loss in a rising main is usually calculated with the Hazen Williams formula using peak flow, the pipe's internal diameter, its length and a roughness coefficient around C = 140 for ageing PE sewer mains. Add about 10% for fittings, then add static lift and residual head to get the pump's duty head.
What velocity should a sewer rising main run at?
A sewer rising main should typically run at about 0.7 to 0.8 m/s or more at design flow so solids do not settle, and below about 2 to 2.5 m/s to limit friction loss and surge. The governing water authority or project specification may set its own limits.
Are grinder pumps better for long rising mains in Australia?
Grinder pumps are generally the better choice for long, small bore rising mains in Australia, because they develop higher head at lower flow and reduce solids to a slurry that stays in suspension in a small pipe. Cutter and vortex pumps suit shorter mains with higher flow and lower head.
What size pipe should a sewer rising main be?
A sewer rising main should be the size that keeps velocity at about 0.7 m/s or more at peak flow while holding friction to a level the pump handles in the middle of its curve. For a 1.5 L/s commercial duty over 400 metres, DN63 PE gives about 0.72 m/s and 5 metres of friction, while DN50 more than triples the friction.
Send us your drawings
Send us the hydraulic drawings, or the peak flow, rising main length, pipe size and material, the long section or static lift, power supply and cover class. We will check the main, select the pumps and controller and return a supply quote, usually within 24 to 48 hours. Payment is required before dispatch, with fast dispatch and delivery to site Australia wide, freight quoted per project.
Email sales@waternex.com.au or call 1300 930 847. For a quick first pass on tank and duty point, use the pump station sizing calculator.
This guide is general technical information for Australian builders, contractors and hydraulic consultants. The worked example is illustrative and is not a substitute for a hydraulic design for a specific site. Water authority requirements govern rising main design, velocity, odour control and connection where they apply. Plumbing work must be carried out by a licensed plumber and electrical work by a licensed electrician.