Pulse-width modulation (PWM) has become the default way to hold a constant application rate while a sprayer changes speed. Instead of throttling the pump, the controller keeps pressure steady and flips a solenoid open and shut many times a second; the fraction of time it is open — the duty cycle — sets how much liquid actually lands. It is elegant, and it works beautifully with the right nozzle. The question of pwm spray system hollow cone nozzle compatibility is whether a hollow cone pattern can hold its shape while the solenoid is chopping the flow underneath it. The short answer: it can, but only inside a pressure and frequency window you have to respect.
What PWM Actually Does to the Liquid
A PWM system does not reduce flow by lowering pressure. It keeps line pressure roughly constant and gates the flow with a fast solenoid. At 80% duty the valve is open most of the time; at 20% it is barely open. The average flow tracks the duty cycle, so the same nozzle delivers a precise rate whether the rig is crawling or flat out.
That is the benefit and the catch in one. Because pressure stays up, the nozzle still forms a good pattern during the open part of each pulse. But between pulses the flow stops, and at the start of the next pulse the nozzle has to re-form its pattern from zero. A hollow cone is the pattern most sensitive to that restart, because it depends on a stable swirl to throw liquid into a ring.
Why Hollow Cone Is the Sensitive One
A hollow-cone nozzle forms its donut by spinning the liquid in a swirl chamber or by a tangential entry (spiral nozzles make hollow cone the same way, with the ramp acting as the swirl path). The ring only appears once the swirl is established and the pressure is high enough that the liquid leaves the edge instead of dribbling. Below a minimum pressure the pattern collapses into a weak stream or a ragged spray, and there is no center fill to hide the failure the way a full cone would.
So under PWM, two things have to stay true through every pulse:
- The pressure during the open part of the cycle must clear the nozzle’s minimum pattern pressure.
- The pattern must re-form fast enough that the closed portion of the cycle is a small fraction of the pulse, or you spend too much time spraying nothing.
If either fails, the hollow cone spends part of each cycle not presenting its ring — and the gas or target sees gaps.
The Pressure Floor Is the First Gate
The single most important number for pwm spray system hollow cone nozzle compatibility is the pressure floor. Pick a hollow cone nozzle whose stable ring forms at or below the pressure your PWM system holds. If your system runs at 3 bar and the nozzle needs 4 bar to make a clean ring, you will never see a good pattern, PWM or not.
Spiral nozzles help here in dirty service, because their open path forms a pattern at lower pressure than a fine vane swirl chamber — but a hollow-cone spiral still has a minimum, and you must confirm it against the operating pressure, not the peak. Under PWM the valve sees the line pressure; size the nozzle so that pressure is comfortably above its floor across the whole duty range you will use.
Duty Cycle: Do Not Go Too Low
Duty cycle is the second gate. At very low duty — say 10–15% — the valve is closed most of the time. Even if the pattern is perfect during the open slice, the average spray is mostly gap, and any delay in re-forming the ring eats into the already-short open window. Most hollow cone nozzles under PWM stay usable down to roughly 20–30% duty, but below that the pattern quality and the effective rate both suffer.
The practical rule: set your PWM system’s minimum duty to the point where the hollow cone still re-forms cleanly, and let rate changes happen above that floor. If you need very low rates, drop to a smaller nozzle and run it at higher duty rather than choking a large nozzle to a few percent.
Pulse Frequency vs Pattern Refresh
The solenoid flips at a frequency — often tens to low hundreds of hertz depending on the controller. The nozzle has its own pattern-refresh time: how long after flow starts until the ring is stable. If the pulse is shorter than the refresh time, the nozzle never finishes forming the pattern before the valve closes, and you get a weak, variable spray every cycle.
Compatibility, then, is a frequency match. Faster solenoids and nozzles that form a ring quickly (open-path spiral types refresh faster than tight vane swirls) tolerate higher PWM rates. If your controller runs a high frequency, confirm the nozzle’s refresh is shorter than the open portion of the shortest pulse you will use. Vendors rarely print refresh time, so the field check is simple: watch the pattern at your minimum duty and lowest speed — if it breaks up, the frequency or the duty is outside the window.
Solenoid and Line Effects You Can Hear
Two real-world issues show up once a system is running. First, if the solenoid and nozzle are far apart on a long line, the pressure pulse softens by the time it reaches the nozzle, which can actually help pattern stability but hurts rate precision — keep the valve close to the nozzle. Second, a worn solenoid that does not fully close lets a dribble through during the “off” part, which blurs the duty cycle and shows up as drift in the applied rate. Neither is a nozzle fault, but both get blamed on the hollow cone.
Spiral Nozzles as the Hollow-Cone Option Under PWM
When the service is also dirty or recirculated, a spiral nozzle giving a hollow-cone pattern is often the safest PWM choice: the open path resists clogging, it forms a ring at lower pressure than a vane swirl, and it refreshes quickly. The trade is the one spiral nozzles always carry — a wide, not tightly uniform, droplet distribution. For absorption and gas-contact duties under PWM that is usually fine; for a duty that needs a precise droplet band it is not, and you would pick a vane hollow cone and accept tighter pressure and clogging limits.
Spiral nozzles and spiral jet variants both sit in this family; the jet form trades the ring for a more directed stream when the duty is a focused wash rather than area coverage. Matching the form to the PWM window is the same exercise — confirm pressure floor, minimum duty and refresh.
The spiral nozzle product range lists angle, flow and the low-pressure band per pattern, which is what you need to confirm the floor before you commit a controller to a duty range.
A Pre-Install Compatibility Check
- Note the line pressure your PWM system holds, and the solenoid frequency.
- Pick a hollow cone nozzle whose stable ring forms below that pressure.
- Set the controller’s minimum duty above the point where the ring re-forms.
- Confirm pulse-open time exceeds the nozzle’s pattern refresh at that duty.
- Field-check the pattern at lowest speed and lowest duty; if it breaks, raise duty or drop nozzle size.
If you are unsure where your PWM system’s window actually sits, send the controller model, line pressure and the rate range you need. The engineering desk will match a hollow-cone nozzle — spiral or vane — to the pressure floor and duty cycle so the pattern holds through every pulse.