When spray performance is “off,” the first instinct is usually to turn the pressure up or down. That can help, but it also changes multiple things at once: droplet size, flow rate, spray angle/coverage, and impact. Meanwhile, the spray pattern type (flat fan vs. full cone vs. hollow cone, etc.) is primarily driven by nozzle design, not by the pressure knob.

This Spray Fact breaks down what actually changes when you adjust pressure, swap nozzle size, or change spray pattern, and offers practical rules of thumb you can use in the field.

► First, align on the terms (so you troubleshoot the right “knob”)

• Spray pattern = the shape of the spray footprint (flat fan, full cone, hollow cone, solid stream, etc.). Pattern is heavily influenced by nozzle outlet shape, internal shape (swirl parts/chambers), how liquid is introduced (axial vs. tangential), and liquid properties like viscosity and specific gravity.
• Spray angle = how wide that pattern opens (e.g., 15°, 40°, 80°, etc.). Angle can shift with operating conditions (pressure, viscosity, distance/trajectory).

Real sprays are polydisperse (a range of droplet sizes). For many industrial processes (evaporative cooling, absorption, gas cooling), the total droplet surface area matters, so Lechler often references Sauter Mean Diameter (SMD / D32), which relates volume-to-surface-area equivalence of the spray.

► The 3 main levers and what they change

What pressure typically changes:

1. Flow rate (single-fluid nozzles): For most single-fluid nozzles, doubling flow requires ~4x the operating pressure (Lechler notes an exception for axial-flow full cone nozzles). This implies the common square-root-style behavior between flow and pressure for many nozzles.
2. Droplet size: Higher operating pressure generally produces finer droplets.
3. Impact: Increasing operating pressure correlates with increased impact at the target.
4. Spray angle/coverage: Spray angle can change with pressure. Lechler notes that at low- or high-pressure levels, the spray angle can be smaller than at the nozzle’s optimum designed operating pressure.

Practical takeaway: Pressure is a fast way to “trim” droplet size and coverage, but it also changes flow and impact. Sometimes enough to create overspray, drift/mist, or wasted liquid if you’re using pressure as a blunt instrument.

If you keep the same pattern family but change nozzle size (capacity/orifice):

• Droplet size: Smaller nozzle bore tends to produce finer droplets (all else equal).
• Flow rate: Nozzle capacity selection directly affects flow, and pressure still governs flow behavior for single-fluid nozzles.
• Impact: Higher flow and/or pressure increases impact (if distance stays constant).

Practical takeaway: If the system is flow-limited or you must keep the same pump curve/pressure window, nozzle sizing is often the cleaner solution than “forcing it” with pressure alone.

Changing the nozzle type changes the spray footprint and often droplet behavior.

A few Lechler-based anchors:

• Hollow cone nozzles are noted as producing the smallest droplet size of any purely hydraulic nozzle (with axial designs producing particularly fine droplets compared to tangential).
• Full cone nozzles are intended to spray fully within a circular area for full coverage.
• Flat fan nozzles provide a narrow line of spray, often chosen when a sharply defined spray is needed for concentrated impact/cleaning.
• Pneumatic (twin-fluid) atomization uses gas + liquid mixing to break liquid into finer droplets; Lechler notes pneumatic flat fan atomizing nozzles can produce extremely fine droplets and spray angles up to ~80°.
• Solid stream nozzles are built for maximum jet power/impact rather than atomized spray.

Practical takeaway: If the application needs a fundamentally different footprint (line vs. ring vs. full circle) or a step-change in droplet fineness, change the nozzle pattern/type. Don’t expect pressure to “transform” one pattern into another.

► The “what actually changes” matrix (rules of thumb)

If you change pressure (same nozzle)

You are likely changing:

• Droplet size (↑ pressure → finer droplets)
• Flow rate (nonlinear; commonly “square-root style” for many single-fluid nozzles; Lechler notes ~4x pressure to double flow for most, except axial-flow full cone)
• Impact (often increases with pressure)
• Spray angle (can vary; extremes can reduce angle vs. optimal designed pressure)

What you are not changing:

• The nozzle’s fundamental pattern family (flat fan won’t become a full cone)

If you change nozzle size (same pattern family)

You are likely changing:

• Flow capacity (directly)
• Droplet size tendency (smaller bore → finer droplets)
• Impact (via flow and/or pressure choices)

If you change nozzle type / pattern

You are changing:

• Footprint geometry and distribution (line vs. circle vs. ring)
• Typical droplet fineness potential (e.g., hollow cone hydraulic tends finer than full cone; pneumatic atomization can go very fine)

Don’t forget the “silent” variable: the liquid

Two liquid properties show up repeatedly in Lechler guidance:

• Viscosity: Higher viscosity tends to resist atomization, can reduce spray angle/flow rate, and can even create filaments instead of a proper spray at extremes; Lechler notes performance charts are based on water (~1 cP) and that nozzle type selection should consider viscosity limits.
• Specific gravity/density: Lechler notes that flow rate varies with medium density (specific gravity relative to water).

Rule of thumb: If you changed chemical concentration, temperature, or the product itself, you may have “changed the nozzle” without touching the nozzle.

Field-side decision shortcuts (practical rules of thumb)

Use pressure adjustments when…

• You need a small-to-moderate trim in droplet size and coverage and can tolerate the associated change in flow/impact.
• You are operating below the intended pressure and need the pattern to “open up” toward its designed behavior (but avoid living at extremes).

Use nozzle resizing when…

• You must hit a target flow rate without forcing large pressure swings (remember: 4x pressure for ~2x flow is a big energy move).
• You need to adjust impact/coverage by managing flow while keeping the same pattern family.

Use a different nozzle pattern/type when…

• The application requires a different footprint shape (line vs. full circular coverage vs. ring).
• You need a step-change in droplet fineness (e.g., hollow cone hydraulic for finer droplets, or pneumatic atomizing for extremely fine droplets).

If viscosity is high…

• Lechler notes single-fluid nozzles generally work best below ~100 cP, with twin-fluid options recommended as viscosity rises; internal vs. external mixing guidance appears around ~300 cP in Lechler’s Spray Fact on viscosity.

► Close: the fastest way to stop chasing knobs

If you’re repeatedly adjusting pressure to fix coverage, drift/mist, or uneven results, it’s often a signal that:

• the nozzle pattern family is wrong for the footprint, or
• the nozzle size is wrong for the available pressure/flow window, or
• the liquid properties changed (viscosity/density/temperature).

Lechler’s nozzle selection guidance consistently ties spray outcomes back to droplet size, spray angle, viscosity, and pattern choice, so you can correct the cause, not just the symptom.