NEWDOSE Dosing Pump Not Pumping? What to Check on Solenoid and Mechanical Models

"The pump keeps clicking, but the tank level never drops." That's one of the calls we get most often. When a NEWDOSE dosing pump won't pump, the first step isn't to strip it down. It's to work out whether you have a solenoid pump or a mechanical diaphragm pump, because they're built differently and the checks differ. Below we go through the common causes in the order the manuals list them.

First, Is the Pump Actually Running?

On a solenoid NEWDOSE dosing pump, the power light comes on when it's energized. Press Start/Stop and the red working light flashes at the stroke rate. If the lights are off or not flashing, you have a power or control problem, not a suction problem. Sort out the electrics first.

On a mechanical NEWDOSE dosing pump, check that the motor turns and the pushrod moves. If the motor runs but the stroke knob sits at 0%, you'll get nothing out. Plenty of people set the knob to 0% for the no-load run during commissioning and forget to turn it back up.

Only when the pump is clearly moving but not delivering are you looking at the priming problems below.

Solenoid Models: Why a NEWDOSE Dosing Pump Won't Prime

Every solenoid NEWDOSE dosing pump in the DFD, DP, DM and DC series shares the same design, and the manual lists seven causes under "pump cannot draw liquid". Here they are, from easiest to hardest to check:

1. Air lock: air in the head means the diaphragm is pushing gas, not chemical. Open the bleed valve and purge it;
2. Suction lift too high: the manual gives a 2 m suction lift. If the height between pump head and liquid level exceeds that, the pump can't work properly, and the only fix is to mount it lower;
3. Leaking suction side: check seals and quick connectors, since even a small air leak in the suction line stops priming;
4. Blocked foot valve: sediment from the tank bottom has coated the strainer, so clean the strainer and foot valve;
5. Blocked head or debris inside: remove and clean the head and valve assemblies;
6. Valves assembled wrongly: after cleaning, upper and lower valves get swapped or parts left out, so reassemble per the manual;
7. Chemical too viscous or prone to gassing: switch to flooded suction with the pump below the liquid level.

For gassing chemicals such as sodium hypochlorite and hydrogen peroxide, the manual also recommends mounting the pump below the liquid level. When a NEWDOSE dosing pump on that kind of duty won't deliver, check for an air lock first. Purging usually brings it back.

Purging air the right way

If the head has a bleed valve, start the pump and open the valve half a turn. Chemical floods the head quickly; close the valve once liquid starts coming out. Run a short tube from the bleed valve back to the tank so nothing splashes.

If there's no bleed valve, disconnect the discharge tube from the injection valve at the injection point, wait for chemical to fill the tube, then reconnect it.

It primes, but output is low

That's not quite "no dosing", though on site it often gets lumped in. The manual lists debris in the head, outlet pressure too high, chemical too viscous, and a failed solenoid or control board. If outlet pressure exceeds the nameplate rating, the only answer is a higher-pressure model. A failed solenoid goes back to the factory; don't open it yourself.

Mechanical NEWDOSE Dosing Pump Models: Suction Line and Check Valves

For NDJ, NDWS, NDWL, ND1000, ND2000 and HND mechanical diaphragm pumps, the manual boils "no discharge at all" down to three causes:

• Suction lift too high: lower the pump and cut down bends and valves;
• Blocked suction line: clean it out;
• Air leak on the suction line: tighten or replace the flange gaskets.

Keep suction lift within 2 m here too, and ideally put the pump inlet below the lowest tank level so chemical flows in under gravity. The suction line should be short, straight and completely airtight. Once it's installed, check for leaks with soapy water.

Check valves fitted backwards pump the wrong way

When you reassemble check valves after cleaning, follow the drawing exactly. The manual is clear that a wrongly fitted check valve can stop discharge entirely, or even pump liquid backwards from outlet to inlet.

One old habit to drop: these check valves seal on an end-face O-ring, so wrapping PTFE tape on the thread can stop it compressing properly and cause leaks. On NDJ pumps, don't overtighten the valves into the head either, or you risk cracking it.

When flow is low rather than zero

If a mechanical NEWDOSE dosing pump delivers but not enough, check for debris in the check valves, worn valves that don't close fully, and a deformed diaphragm, then check motor speed and supply voltage. For thick chemicals, switch to a pump suited to high viscosity.

Prevention

Rather than waiting for your NEWDOSE dosing pump to stop delivering, spend a few minutes on routine checks. Watch the tank level, and where possible fit a level switch so the pump stops automatically when the level drops. That way it never runs empty and the line is less likely to draw air. Clean check valves and strainers regularly; the right interval depends on the chemical, so build it from your own experience.

Before storing a solenoid NEWDOSE dosing pump for a long period, circulate clean water for 10 to 20 minutes, then switch it off. When restarting a mechanical pump that has stood for more than a week, set the stroke to 0% and run it unloaded for a few minutes before normal use.

Conclusion

Troubleshooting a NEWDOSE dosing pump comes down to a sequence. Confirm the pump is moving, check the suction side for air leaks, blockages and excess lift, then check valve assembly, and only then suspect the diaphragm or drive. Solenoid pumps are usually air locked and just need purging; mechanical pumps usually have suction line or check valve issues. Follow that order and most problems get solved on site.

FAQ

Does a NEWDOSE dosing pump that won't deliver always have a broken diaphragm?

No. The diaphragm is near the bottom of the list. Purge air, then check the suction line, foot valve and check valves. Only consider the diaphragm if those don't fix it.

My NEWDOSE dosing pump stopped priming after a tank change. Why?

Most likely air entered the suction tube during the swap, or the new tank is shorter and the suction lift increased. Purge again and measure the height between pump head and liquid level.

Is lower flow normal once the discharge is reconnected to the injection point?

Yes. The injection point adds back pressure, so flow is a little lower than into open air. For accurate dosing, calibrate with a measuring cylinder under real conditions and set the pump by the measured figure.

Chemical keeps flowing on its own at a low-pressure injection point. What now?

That's siphoning, common when the tank level is above the injection point. Fit a back pressure valve on the outlet and adjust until the free flow stops.

Can I service a NEWDOSE dosing pump head myself?

Cleaning the head, foot valve and check valves per the manual is fine. Stop the pump, release pressure and drain residual chemical first. The internal solenoid and control board should be left to factory-authorized service staff.

Still not dosing after all that? Send us the model, chemical and installation layout through our contact page and we'll help work it out.