Why Dripper Selection Matters: Operating Pressure, Closing Pressure & Flow Rates Explained

Why Dripper Selection Matters: Operating Pressure, Closing Pressure & Flow Rates Explained

Whether you're running a commercial strawberry operation in coir troughs or managing a multi-hectare raspberry crop in pots, the drippers you choose can make or break your irrigation uniformity. At IrriSmart, we've built our dripper range around three core principles: wide operating pressure ranges, appropriate closing pressures, and matched flow rates for every crop and substrate. Here's why each one matters.

1. Operating Pressure Range — The Foundation of Uniform Flow

Why It Matters

Pressure-compensating drippers are designed to deliver a consistent flow rate across a range of inlet pressures. The wider that operating range, the more tolerant the dripper is to pressure variation along the dripline — which is critical on longer run lengths where friction losses and elevation changes cause pressure to drop from the inlet to the tail end.

A narrow operating range means that drippers near the header may be operating at the top of their compensation window while drippers at the tail end fall below it — resulting in uneven application and stressed plants at the far end of the run.

Our Range at a Glance

Dripper	Operating Pressure Range
Netafim HCNL	1.5 – 3.5 bar
Rivulis Click Tif	0.8 – 4.0 bar
Rivulis SuperTif HDN	1.2 – 3.5 bar
Rivulis SuperTif ND	0.7 – 3.5 bar

The Rivulis Click Tif and SuperTif ND stand out here with lower minimum operating pressures (0.8 and 0.7 bar respectively), making them well suited to gravity-fed systems or installations where inlet pressure is limited. The Click Tif's upper limit of 4.0 bar also gives it the widest overall window — a 3.2 bar span — offering the greatest tolerance to pressure fluctuation across long runs.

Practical Rule of Thumb

As a general guide, calculate your expected pressure at the tail end of your longest run under peak demand. If that figure falls within the dripper's operating range with at least 0.2–0.3 bar of headroom, you're in a safe zone. If not, consider splitting the run or upsizing your supply pipe.

2. Closing Pressure — Managing Slopes and Drainage

Why It Matters

The closing pressure is the minimum pressure at which a dripper remains open. When the system shuts down and pressure drops, drippers close at this threshold. The higher the closing pressure, the sooner the dripper seals — and crucially, the greater the slope the system can tolerate without drippers at the bottom of a run draining the dripline after irrigation.

On sloped ground, a column of water in the dripline creates a hydrostatic head. For every 10 cm of vertical drop, approximately 0.01 bar of pressure is generated. A dripper with a closing pressure of 0.3 bar will therefore hold back drainage on slopes of up to approximately 3 metres of vertical fall before the hydrostatic head exceeds the closing force.

Our Range at a Glance

Dripper	Closing Pressure
Netafim HCNL	0.18 bar
Rivulis Click Tif	0.30 bar
Rivulis SuperTif HDN	0.35 bar
Rivulis SuperTif ND	0.15 bar

When You Need LPD or DNL Valves

If your field or glasshouse has a vertical fall greater than what the dripper's closing pressure can hold, you'll need to install LPD (Low Pressure Drain) or DNL valves along the dripline to prevent post-irrigation drainage and the associated problems — air ingress, uneven re-wetting at the next irrigation event, and potential root zone disturbance.

A few key points to keep in mind:

• 0.3 bar closing pressure (Click Tif) handles up to ~3 m of vertical drop without additional valves

• 0.35 bar (SuperTif HDN) handles up to ~3.5 m — the most slope-tolerant in our range

• 0.15–0.18 bar (SuperTif ND, HCNL) are better suited to flatter installations or where LPD/DNL valves are already planned into the design

• As a general recommendation, install 3 LPD/DNL valves per 100 m run on sloped sites

• Bear in mind: every valve adds resistance, so factor the cumulative pressure loss into your system design — particularly on longer runs where you may already be working close to the lower end of the dripper's operating range

The relationship between closing pressure and valve frequency is a balancing act. A higher closing pressure dripper may eliminate the need for valves entirely on moderately sloped sites, simplifying installation and reducing ongoing maintenance.

3. Flow Rates — Matching Output to Crop, Substrate and Container

Why It Matters

Getting the flow rate right is about matching water delivery to the uptake capacity of the root zone. Too fast and you risk runoff, channelling through the substrate, and leaching of nutrients before roots can absorb them. Too slow and you may not achieve the target volume within your irrigation window, particularly during peak summer demand.

The right flow rate depends on:

• Substrate type — coir, rockwool, perlite, and soil all have different infiltration rates

• Container or bag volume — smaller containers need lower flow rates to avoid overflow

• Crop water demand — high-transpiration crops like strawberries and raspberries in peak summer can require multiple short irrigation events per day

• Dripper spacing — more drippers per metre at a lower flow rate can give better lateral distribution in long bags or troughs

Recommended Configurations

Coir-grown strawberries in 1 m bags or troughs:

Configuration	Drippers/metre	Flow Rate per Dripper
Option A	5	1.1 – 1.3 l/hr
Option B	4	1.6 – 2.2 l/hr

Both configurations deliver a similar total volume per metre of trough, but Option A distributes water more evenly across the bag length — beneficial in longer troughs where lateral water movement in coir is limited. Option B uses fewer drippers, reducing installation time and component cost, and may be preferable where substrate distribution is more uniform.

Coir-grown raspberries in pots:

Configuration	Drippers/pot	Flow Rate per Dripper
Standard	2	1.6 – 2.2 l/hr

Two drippers per pot ensures even wetting from both sides of the root ball, reducing the risk of dry zones developing in the coir. The 1.6–2.2 l/hr range gives enough flow to achieve target volumes within a short irrigation pulse without overwhelming the pot's drainage capacity.

Choosing the Right Dripper — A Quick Decision Guide

Situation	Recommended Consideration
Long run lengths (>80 m)	Prioritise wide operating pressure range
Sloped site (>2 m vertical fall)	Choose higher closing pressure or plan LPD/DNL valves
Flat glasshouse, short runs	Lower closing pressure drippers are cost-effective
Gravity-fed or low-pressure systems	SuperTif ND or Click Tif (low minimum operating pressure)
High-density strawberry troughs	5 × 1.1–1.3 l/hr for even distribution
Raspberry pots	2 × 1.6–2.2 l/hr per pot

Need Help Specifying Your System?

Every site is different. If you're unsure which dripper is right for your run length, slope, crop, or substrate, get in touch with the IrriSmart team. We're happy to work through the hydraulics with you and recommend a solution that delivers uniform irrigation from header to tail.