How to Size a Mainline for Sumi Soaker Irrigation — Pipe Sizing Guide

Your Sumi Soaker tubing connects to a water source. For small setups — one or two short beds — a garden hose does the job. But the moment you're running multiple beds, longer runs, or feeding tubing from a water source more than 50 feet away, you need a mainline.

A mainline is simply a pipe that carries water from your source to where the tubing starts. It's the backbone of your irrigation system. The pipe diameter you choose determines how much water it can carry, which in turn determines how many Sumi lines you can run and how far away from your water source you can get before pressure drops too low.

This Sumi Soaker Mainline Sizing guide covers the two most common mainline materials — poly tubing and PVC pipe — and shows you exactly how many Sumi R-Wide or Mark II lines each diameter supports.

You can use our calculator to size your mainline pipe and see how many Sumi lines it can run. Sumi Soaker Mainline Calculator

The mainline carries pressurized water from your source (hose bib, well pump, municipal connection) to one or more takeoff points along your growing area. At each takeoff, a tee fitting branches off to a pressure regulator and then into your Sumi tubing.

The mainline itself doesn't water anything. It's the supply highway. The Sumi tubing is the last mile.

Three things determine what size mainline you need: 

1. How many Sumi lines you want to run at the same time
2. What product you're running (R-Wide or Mark II)
3. How far the mainline runs from your water source.

Poly tubing is flexible, sold in coils, and connects with barb fittings and hose clamps. It's the most common mainline material for market gardens and small farms because it's easy to install — no gluing, no special tools. You unroll it, cut it, push barb fittings in, and clamp them down. It can be buried or laid on the surface.

Poly tubing is available from 1/2 inch up to 2 inches at most irrigation suppliers. For Sumi Soaker mainlines, 3/4 inch is the minimum useful size and 1 inch or larger is recommended for most installations.

PVC is rigid, sold in straight sticks (typically 10 or 20 feet), and connects with solvent-welded (glued) fittings. It's the standard for permanent, buried irrigation mains. PVC carries more water per dollar than poly at the same diameter, and the fitting ecosystem is enormous — tees, elbows, reducers, threaded adapters, and ball valves are available at any hardware store.

PVC is the better choice for permanent installations, long runs, and systems with many takeoff points. Most growers buy PVC locally rather than ordering it online since shipping rigid pipe is impractical.

Every pipe has a maximum flow rate determined by its inside diameter. Push water through too fast and you get excessive friction loss, pressure drop, and water hammer (the banging sound when valves close quickly). The standard safe velocity limit for irrigation pipe is 5 feet per second.

PVC has slightly lower flow capacity than poly at the same nominal size because Schedule 40 PVC has thicker walls, which means a smaller inside diameter.

This is the core question: given a pipe diameter, how many Sumi lines can you feed simultaneously?

There are two ceilings to consider. 

First, the pipe's flow capacity — water can only move through it so fast. 

Second, the pressure regulator's 20 GPM maximum — a single Senninger PMR-MF regulator can pass up to 20 GPM regardless of how large the pipe is. 

If your total demand exceeds 20 GPM, you need multiple regulators or zones.

*A single 150 ft R-Wide line draws 19.1 GPM — just under the regulator's 20 GPM maximum. Each 150 ft line requires its own regulator.

*Regulator-limited at 20 GPM. The pipe can carry more, but a single regulator caps at roughly 11 simultaneous 50 ft lines, 5 lines of 100 ft, or 5 lines of 150 ft. Beyond that, you need a second regulator on a separate zone.

Mark II's low flow demand means even a 3/4" mainline supports useful configurations. For R-Wide, 1" poly is the practical minimum and 1-1/2" or larger is recommended for anyone running more than one line at a time.

A mainline isn't just about flow capacity — it also has to deliver enough pressure at the far end for the regulator to work. The Senninger PMR-30 (R-Wide) needs at least 35 PSI at its inlet. The PMR-12 (Mark II) needs at least 17 PSI. If friction inside the mainline eats too much of your source pressure before the water reaches the regulator, the system won't perform.

Larger pipe loses less pressure over the same distance because water moves through it more slowly. Here's what a 20 GPM flow looks like across different pipe sizes over various distances:

If your source pressure is 50 PSI and you're running 400 ft of 1" poly at 20 GPM, you lose roughly 48 PSI to friction — leaving only 2 PSI at the far end. That's not enough for either regulator. But 2" poly over the same distance loses only 2 PSI, leaving you 48 PSI — more than enough.

The takeaway: for short runs under 100 ft, 1" pipe works for most setups. For runs over 200 ft, go to 1-1/2" or larger. For runs over 400 ft, 2" is strongly recommended.

Small Garden (1–4 beds, under 100 ft from source)

If you're running a few short beds close to your water source, 3/4" or 1" poly is sufficient. Mark II runs comfortably on 3/4". R-Wide needs at least 1" for a single 100 ft line. Connect your Sumi Mainline Connector directly to the poly with a barb-to-threaded adapter.

Mid-Size Market Garden (4–10 beds, 100–300 ft from source)

This is where 1" or 1-1/4" poly makes sense. You'll run one or two R-Wide lines at a time (zoning the rest), or several Mark II lines simultaneously. Install ball valves at each takeoff point so you can control which lines are active.

Large Layout (10+ beds or 300–700 ft from source)

Go with 1-1/2" or 2" poly (or PVC if you're burying it permanently). At these distances, friction loss is the primary concern — and only larger pipe keeps enough pressure at the far end. A 2" mainline at 700 ft from a 60 PSI source still delivers 56+ PSI at the last hydrant.

For large layouts, plan to zone your system. Even with a 2" mainline, you'll rarely run every Sumi line simultaneously — the regulator's 20 GPM cap means you feed a few lines at a time and rotate through zones.

At each point where you want a Sumi line, you need four things: a tee fitting to branch off the mainline, a ball valve for on/off control of that line, a pressure regulator to step down to the correct operating pressure, and the Sumi tube start connector.

The Sumi Soaker Mainline Connector includes the Senninger pressure regulator with NPT pipe thread fittings and a 3/4" to 1" reducer bushing. It connects to the outlet side of your ball valve. If your header or tee is larger than 1", you'll need a reducer bushing to step down to 1" threads.

For poly mainlines, use barb tees with hose clamps. For PVC mainlines, use slip or threaded tees depending on your preference.

Most growers can't run every Sumi line at the same time — and that's fine. Professional irrigation systems are designed to run in zones. Each zone is a group of lines that runs together, and you cycle through zones sequentially.

A simple zoning approach: install a ball valve at every takeoff. To irrigate, open the valves for one zone, run water until the beds are saturated, close those valves, and open the next zone. For germination watering, you might run each zone for 15–30 minutes before moving to the next.

The total number of zones depends on your available supply flow divided by the flow demand per zone. If your pump delivers 20 GPM and each R-Wide 100 ft line needs 12.7 GPM, you run one line per zone. If you're running Mark II at 3.6 GPM per 100 ft line, you can run five lines per zone through a single regulator.

The mainline is the foundation of your Sumi Soaker system. Size it right and everything downstream works as designed. Size it too small and you'll fight pressure drop and flow restrictions for as long as the pipe is in the ground.

When in doubt, go one size larger than you think you need. The cost difference between 1" and 1-1/2" poly is modest compared to the cost of ripping out undersized pipe and starting over. And if you're running more than 200 feet from your source, 2" pipe is almost always the right call.

You can use our calculator to size your mainline pipe and see how many Sumi lines it can run. Sumi Soaker Mainline Calculator

Use our free online tools to get a personalized recommendation:

Sumi Soaker System Planner — Tells you what tubing and how many rolls you need based on your bed layout.

Sumi Soaker Water Supply Calculator — Tells you whether your water supply can handle the setup you need, and what to do if it can't.

Both tools are available at shop.moderngrower.co.

Questions? Email us or use the chat on our website. We'll walk you through it.

The Sumi Soaker R-Wide and Mark II are available in the US from Modern Grower. Visit shop.moderngrower.co to see the full product line, starter kits, and accessories.

Ready to figure out what you need? 

Use our System Planner to size your setup and our Water Supply Check to verify your pressure and flow. Or reach out to us directly at hello@moderngrower.co or 877.850.1555 — we're happy to help you design a system that fits your layout.