How to Replace a NEWDOSE Degassing Valve: Steps and Seal Checks

A degassing valve that won't seal, a knob that keeps weeping chemical, or a valve that never lets the air out: in all three cases it is time for a new one. The job itself is simple. Skip the preparation or the seal checks afterwards, though, and the pump leaks just as badly as before, or you end up damaging the thread in the head.

This guide uses the NEWDOSE DFD, DP, DM and DC solenoid diaphragm pumps as the example, and follows the same order we walk customers through on site.

Where the Degassing Valve Sits and What It Does

On these solenoid pumps the degassing valve is mounted on the side of the pump head. Inside, the head has two valve sections at the top and two at the bottom. The upper valve section 2 has a small vent port, and that port is how the degassing valve connects to the inside of the head. When gas collects in the head, opening the valve lets gas and liquid escape.

The manual uses it at two points. At first start-up, open the degassing valve half a turn so liquid fills the head quickly, then close it as soon as liquid comes out. During flow calibration, start the pump, open the valve to clear the bubbles, close it, and only then start timing.

If the degassing valve no longer closes properly, every stroke sends part of the dose back through it. Output drops and calibration never comes out right. When a site reports a pump that is clicking but under-dosing, check this valve early. A wet ring around the knob, or a return tube that drips constantly, tells you straight away.

Three Things Before You Change the Degassing Valve

The NEWDOSE manual is clear about preparation before any teardown, and we insist on it on site:

1. Switch off the power to the pump, don't just press stop.
2. Disconnect the lines attached to the pump head, releasing pressure in them first.
3. Drain the pump and head. You can turn the pump upside down, then circulate clean water through it.

If the chemical is toxic or corrosive, release discharge line pressure first, neutralize or flush out the residue, wear gloves and goggles, and keep the area ventilated.

Removing the Old Valve and Fitting the New One

Once that is done, work in this order:

1. Pull off the tube that runs from the degassing valve back to the tank.
2. Unscrew the old valve from the side of the head. Go slowly, there may still be a little liquid inside.
3. Look at the mounting hole and sealing face in the head for crystals or scratches.
4. Fit the new degassing valve, turn it home by hand, then snug it gently. Plastic threads don't need force.
5. Reconnect the return tube and put the other end back into the tank or a collection container.

Use a genuine NEWDOSE part. The manual says repairs should use original parts, otherwise safe operation of the pump is affected.

While the old valve is out, check the upper valve

The vent port is in upper valve section 2, and with crystallizing chemicals that small hole blocks easily. If a new degassing valve still won't release air, take the upper valve out and clean it.

When you do, remember that upper valve 1, upper valve 2, lower valve 1 and lower valve 2 look much alike. Only upper valve 2 has the vent port, so don't swap it with a lower section on reassembly.

Seal Checks After Reassembly

Fitting the valve is not the end of the job. Put the suction hose into clean water, start the pump, open the degassing valve half a turn, and close it once liquid flows steadily. Then watch these points:

• the base and knob of the degassing valve, for any weeping;
• the upper and lower valve nuts, tightening any that have worked loose;
• the edge of the pump head. If it leaks, tighten the head bolts as the manual specifies.

Head bolt preload depends on the pump frame: 2.16 N·m for M and HX, 2.41 N·m for NX and GX, and 2.90 N·m for the 30L and 50L sizes. Over-tightening can crack a plastic head, so work to these figures rather than by feel.

If a seal is missing, replace it. If seals or the head itself are corroded, don't improvise. Contact the manufacturer.

NEWDOSE Dosing Pump Repairs: What You Can Do Yourself

External parts such as the degassing valve, tubing, foot valve and injection valve can generally be replaced by users. The inside of the pump is different. The manual requires internal repairs to be done by qualified personnel authorized by the manufacturer, and a failed drive unit such as the solenoid goes back to the factory.

For routine care of a NEWDOSE dosing pump, the manual recommends checking head bolt tightness and the condition of all seals at least every six months, more often with corrosive liquids. The recommended periodic check interval is 500 hours of continuous running or 1000 hours of cumulative running.

On the mechanical diaphragm pumps, the manual recommends a degassing valve at the pump outlet to help start-up. Their check valves seal on an end face O-ring, so don't wrap them in PTFE tape, which stops the O-ring seating and causes leaks. Don't over-tighten the check valve into the head either, as that can damage the head.

Conclusion

Replacing a degassing valve is mostly about order: power off, release pressure, drain and flush, then remove the old valve, check the vent port, fit a genuine replacement, and finish with a water run to vent and leak test. Torque the head bolts to the figure for your frame size and keep upper valve 2 in its place. Leave internal faults to the manufacturer.

FAQ

Does a leaking degassing valve always need replacing?

Not always. Check that it is fully closed and that no crystals are sitting under its base. If it still leaks after cleaning, or the knob thread is stripped, replace it.

Do I have to remove the pump head?

Usually not. The degassing valve unscrews from the side of the head. You only need to take the upper valve out if the vent port is blocked.

Can I leave the tube off the degassing valve?

Better not. The manual calls for a length of tube from the degassing valve back to the tank or another collection container. Without it, chemical ends up on the floor every time you vent.

The pump still won't prime after the change. What next?

Work through the fault table: suction side seals, correctly assembled valves, suction lift not too high, foot valve not blocked. If there is a lot of gas, vent again.

How often should the head bolts on a NEWDOSE dosing pump be checked?

At least every six months according to the manual, and more often with corrosive chemicals. If you see weeping at the head edge during rounds, retighten to the torque for your frame.

Not sure which frame you have or which degassing valve to order? Send a nameplate photo through our contact page.