Dosing Pump Frequency Setting: What the F on the Display Means

A dosing pump frequency setting tells the pump how many strokes it makes per minute. On many solenoid pumps the display shows this as a number, sometimes with a letter such as F next to it. The letter is usually a mode flag, while the number is the stroke rate in strokes per minute (spm). The exact meaning differs by brand, so check the manual for your model.

This guide is for operators and contractors who inherit a chemical feed skid and need to read the panel quickly. I will use two real examples, NEWDOSE and IWAKI, because their documents are clear about it.

How a solenoid pump turns frequency into flow

A solenoid metering pump moves its diaphragm with an electromagnet. Each pull is one stroke. Flow depends on only two things: stroke length (volume per stroke) and stroke frequency (strokes per minute).

So any dosing pump frequency setting is half of your flow equation. The other half is the stroke length knob. Motor-driven diaphragm and plunger pumps work differently, so do not apply this logic to them.

Dosing pump frequency setting on NEWDOSE DM pumps

The NEWDOSE solenoid pump manual covers the DM series, which accepts a 4-20mA signal. Here is what the display tells you:

• In manual mode the display reads something like "120F". The pump is in manual mode and stopped. Press Start/Stop and it runs at the frequency shown.
• The manual states that when F is displayed, the pump is in manual adjustment mode. The up and down keys change the number, which is the current working frequency.
• In automatic mode the display reads "000A". A flashing A means stopped; a steady A means running, with frequency following the external current.

So on this pump, F is the manual mode flag and the three digits are the dosing pump frequency setting. The DP series, which takes pulse signals, uses H for manual and P for external pulse control instead. Even inside one brand the letters change between series.

The manual also notes that the red indicator flashes at the current working frequency. Watching the light is a quick way to confirm the pump is actually stroking.

Units: strokes per minute and spm

The unit for a dosing pump frequency setting is strokes per minute, written spm in most English documents. IWAKI lists its EHN-R series with a digital controller that sets 1 to 360 spm in one-stroke steps. Combined with stroke length adjustment, that gives a wide flow range. The EHN panel shows the spm value itself, with no F.

Some pumps skip frequency on the display and show flow directly in L/h or mL/min. ProMinent gamma/X, for example, lets you set the flow in l/h. On a panel like that, the reading is already flow, so stop looking for a stroke rate.

Figure 1: IWAKI EHN-YN series electromagnetic metering pump. Image source: IWAKI official website

Converting the dosing pump frequency setting to flow

The NEWDOSE manual gives this formula: working flow = maximum flow ÷ 120 (or 160) × current working frequency. The 120 or 160 is the maximum frequency of that model; check the nameplate and manual.

A simple way to think about it: on a pump with a 120 spm maximum, a display of 60 at full stroke length gives about half the rated flow. If the stroke length has also been reduced, multiply by the stroke percentage as well.

Treat the result as an estimate. Back pressure and viscosity shift the real number, so confirm any new dosing pump frequency setting with a calibration column. Our guides on stroke frequency calculation and solenoid pump flow adjustment walk through the arithmetic.

Common mistakes when reading the display

These three come up again and again on site:

1. Treating F as a fault code. The pump is simply stopped in manual mode. One press of Start/Stop and it runs.
2. Reading frequency as flow. A display of 120 is not 120 liters per hour, and the dose ends up far off.
3. Changing the manual number while in external mode. In A or P mode the manual dosing pump frequency setting is ignored. Press A/M to return to manual first.

If you run NEWDOSE pumps, see our DFD vs DP comparison. For IWAKI key sequences, read the EHN control panel guide. Model ranges are on the NEWDOSE brand page and in our solenoid metering pump category.

Checking an unfamiliar pump

When the manual is missing, you can still work out the panel:

1. Note the model and maximum flow on the nameplate. Some nameplates also show the maximum stroke rate.
2. Press the mode key (A/M on NEWDOSE) and watch whether the letter changes. A letter that toggles is a mode flag.
3. Count the indicator flashes for one minute with a stopwatch. If the count matches the display, the number is the dosing pump frequency setting.
4. Catch the output in a graduated cylinder or calibration column for one minute and compare it with your estimate.

If the numbers still do not line up, ask the manufacturer for the manual matching your pump version rather than guessing.

Conclusion

The F on a solenoid pump display depends on the brand. On NEWDOSE DM pumps, F after the number means manual adjustment mode and the digits are the working frequency; A means current control, while the DP series uses H and P. Most pumps measure frequency in strokes per minute. To turn any dosing pump frequency setting into flow, use maximum flow ÷ maximum frequency × current frequency, multiply by stroke percentage, then verify with a calibration column. If you are unsure about a panel, send us a photo through our contact page.

FAQ

What does F mean on a solenoid metering pump?

On NEWDOSE DM pumps it marks manual mode, and the number before it is the stroke frequency. Other brands may use it differently, so check the manual.

Is 120F on the display a fault?

No. On a NEWDOSE DM pump it means manual mode, stopped. Press Start/Stop and it runs at 120 strokes per minute.

What is the unit of a dosing pump frequency setting?

Strokes per minute, usually written spm. IWAKI EHN-R pumps, for example, can be set from 1 to 360 spm.

What if maximum frequency still gives too little flow?

Check that stroke length is at 100%. If both are at maximum and flow is short, the pump is undersized for the job.

Why can't I change the dosing pump frequency setting with the keys?

The pump is probably in external mode, where the 4-20mA or pulse signal controls frequency. Switch back to manual with the A/M key first.