Metering Pump Startup: First Start and Daily Start-Stop Sequence

A metering pump startup comes in two versions. The first start after installation or overhaul needs checks, priming and a gradual ramp to the working setting. The daily start and stop is much simpler, and it rests on one rule: open the valves before starting the pump, and stop the pump before closing the valves. Get that order wrong and the relief valve lifts at best, or the diaphragm and pipework take the pressure at worst.

This metering pump startup sequence applies to solenoid and mechanical diaphragm pumps, and is written for operators and commissioning staff.

Checks before the first metering pump startup

Before a new or overhauled pump runs for the first time, go through these points.

Oil level. Mechanical and hydraulic diaphragm pumps may ship without gearbox oil, or with transport oil only. Check the sight glass and fill to the level in the manual. Solenoid pumps have no gearbox.

Power. Confirm voltage and frequency match the nameplate and the earth is sound. On three-phase motors, check rotation against the arrow on the pump; swap any two phases if it is wrong.

Control mode. Solenoid pumps left in external or pulse mode with no signal connected will not stroke when you press start. Many "dead pump" calls on day one are just this.

Piping. Suction and discharge lines complete, joints tight, no weld debris inside. Flush new lines with water first.

Valves and accessories. Suction and discharge valves ready to open, back pressure and relief valves set, pressure gauge fitted.

Tank. Enough liquid, level switch connected. For the very first run, use clean water before introducing chemical.

First metering pump startup, step by step

1. Open the tank outlet and pump suction valves so liquid floods the suction line.
2. Open the pump discharge valve and the isolation valves around the back pressure valve. Open the injection point valve too.
3. Set stroke low. On a solenoid pump, set frequency low as well.
4. Start the pump and open the priming or bleed valve on the head until liquid flows without bubbles, then close it.
5. Watch the discharge gauge. Once pressure is steady, bring stroke and frequency up to the working setting.
6. Run for a while and check joints for leaks, listen for unusual noise and feel the motor temperature.
7. Calibrate the actual output with a drawdown test.

Priming is the step people skip. With gas in the head, the diaphragm moves but nothing leaves the pump. See how to prime a diaphragm metering pump for details.

When to turn the stroke handwheel

On mechanical diaphragm pumps, adjust stroke only with the pump running. Forcing the handwheel at standstill can damage the mechanism. Loosen any locking screw first and lock it again afterwards.

Do not let it run dry

If the pump will not prime during metering pump startup, do not leave it stroking dry for long. Dry running is hard on diaphragms and valve seats, especially where seals rely on the liquid for lubrication. If it has not primed after a few minutes, stop and find out why. Our article can a metering pump run dry explains the risks.

Daily start and stop

Daily metering pump startup

1. Check the tank level.
2. Open suction and discharge valves and confirm the injection point is open.
3. Start the pump and watch pressure return to normal.
4. Walk the line and look for leaks.

Daily shutdown after a normal metering pump startup

1. Stop the pump.
2. Close the discharge valve, then the suction valve.
3. For long shutdowns, flush the head and lines with clean water, especially with crystallising chemicals such as PAC and sodium hypochlorite.

The most common mistake is starting against a closed discharge valve. A positive displacement pump builds pressure fast. With no relief valve, or one set too high, something will give.

Metering pump startup mistakes we see on site

Relief valve return line isolated. Someone closes the return line valve to stop drips, and the relief valve can no longer do its job.

Cold, thick chemical. Polymer and strong coagulant thicken in winter, which makes a cold metering pump startup slower to prime. Run at short stroke for a while before ramping up.

Chemical changeover without flushing. Two incompatible products meeting in the head can react or crystallise.

Level switch left bridged. A temporary bridge during commissioning is forgotten, and the pump runs dry when the tank empties. See low level alarm setup for wiring and delay settings.

Safety: wear gloves and eye protection with acids, caustic and hypochlorite, and stop the pump and relieve pressure before opening any fitting.

These steps fit most diaphragm pumps; always follow the manual for your model. For spare parts or new pumps, see our diaphragm metering pumps.

Conclusion

A good first metering pump startup means checking oil, power, control mode, piping and valves, starting at short stroke, priming fully, ramping to the setting and calibrating. Every day after that, open valves before starting and stop before closing, and flush before long shutdowns. Tell us your pump model and chemical, and contact our engineers for a start-stop card tailored to your site.

FAQ

Should the first metering pump startup use chemical or water?

Water. Confirm there are no leaks and pressure is normal, then switch to chemical. This matters most with aggressive chemicals.

The gauge does not move after metering pump startup. Why?

Usually gas in the head or a closed suction valve. Open the bleed valve and check the suction side. If it still does not move, check whether a check valve is fitted the wrong way round or stuck.

What is the most common mistake in a metering pump startup?

Starting with the discharge valve closed. Pressure rises very quickly and can damage the diaphragm or pipework.

Do I need to flush after every stop?

Not for short daily stops. Flush before long shutdowns, or when using chemicals that crystallise, such as PAC or hypochlorite.

How often should gearbox oil be changed?

Follow the manual. Typically there is a first change after running in, then changes at set running hours, or sooner if the oil darkens or shows water.