Metering Pumps Finale – The Best of The Best

Congratulations, you’ve reached the series finale on the best metering pumps! As you know, a metering pump must be able to meter and transfer highly accurate, measured amounts of fluid across a range of discharge pressures. You can use a metering pump to transfer viscous liquids, as well as acids, bases, and solvents.

We’ve compared the pros and cons of each type of metering pump during the series, so let’s look at which metering pump works best for a specific application or condition.

Practical flow range

To measure a continuous flow range of a liquid, we look at liters per hour (LPH). The maximum flow range of a pump then determines how much liquid can flow through the pump every hour. The higher the maximum flow range needed, the more your pump requirements change.

For up to 250 LPH requirement, a diaphragm pump would be your best bet. If you’re looking for a maximum practical flow range between 250 to 2200 LPH, you’ll should consider a magnetic drive pump. A sliding vane mag-drive pump can handle a flow range of 2200 LPH, whereas a gear pump can allow a maximum of 4000 LPH. Anything above 4000 LPH can be served by a peristaltic pump.

Practical pressure range

A pump must produce enough pressure differential to overcome the head loss caused by friction, valves, and fittings in the pipe system. The flow range is the volume of water a pump can move at a given pressure.

Practical flow range and pressure range are two very crucial indicators of what type of pump you need. For pressure of 6 – 10 bar, most types of postitive displacement pumps are suitable. Both sliding vane and gear pumps allow a practical pressure range of 10 bar. For pressure ranges up to 16 bar, diaphragm pumps would be best. Lastly, a progressive cavity pump is the only pump in this selection that has a pressure range of up to 20 bar.

Chemical compatibility

If your facility deals with a range of different chemicals, consider diaphragm, gear or sliding vane mag-drive pumps – all three with excellent chemical compatibility. Peristaltic pumps are compatible with most chemicals (but very few solvents), whereas progressive cavity pumps are mostly suited for polymers. See the below chart for more on the specific chemicals that these pumps are suited (or not suited) for.

Common Water Treatment Chemicals	Diaphragm	Peristaltic	Gear	Sliding Vane	Prog. Cavity
Sodium Hypochlorite	Good	Excellent	Excellent	Excellent	Poor
Sodium Hydroxide	Good	Good	Good	Good	Poor
Sodium Bisulphite	Good	Good	Good	Good	Poor
Ferric Chloride	Excellent	Excellent	Poor	Good	Poor
Aluminum Sulphate	Good	Good	Good	Good	Poor
Hydrofluosilicic Acid	Excellent	Poor	Excellent	Excellent	Poor
Sulphuric Acid	Good	Poor	Excellent	Excellent	Poor
Hydrochloric Acid	Good	Good	Excellent	Excellent	Poor
Polymers	Good	Excellent	Poor	Good	Excellent

Turndown capability

Turndown is the ratio of the metering pump’s output. The following example demonstrates how turndown works:

“If a pump is capable of a maximum of 1,000 gallons per hour (gph) and it has a 100-to-1 turndown ratio, then it can be adjusted to a flow rate as low as 10 gph and still perform within its accuracy rating.”

Generally speaking, the standard ratio is 10:1, but some pumps can pump accurately to a much lower value. Peristaltic pumps offer excellent metering range/turndown, while mag-drive or progressive cavity pumps also offer good metering range/turndown capability. If superior turndown is important, steer clear of diaphragm pumps as can suffer from pulse lag.

Pulsation

For a metering pump with minimal pulsation, look no further than a mag-drive gear or vane pump. You can also use a peristaltic pump in a pinch, but avoid large diaphragm pumps, which can suffer from slug dosing or even piping/system damage due to high pulsation (note: this is not an issue for stepper motor pumps with low pulsation).

Slurries/solids handling

Peristaltic and progressive cavity pumps compete for the best metering pump for the wastewater industry, because of their excellent slurry/solid handling capability. Diaphragm pumps can also handle slurries, but this may slow the pump down. Whatever you do, don’t try a mag-drive pump, as gear pumps can’t pump solids and sliding vane pumps are unsuited to slurries or solids.

Viscosity handling

Naturally, with the excellent slurry/solid handling capabilities of the peristaltic and progressive cavity pumps, these pumps are good for handling many different viscosities. While diaphragm and mag-drive pumps are capable of handling applications with high viscosity, they are outmatched by these two when it comes to pumping highly viscous fluids.

Off-gassing

If off-gassing is an issue, avoid the progressive cavity and diaphragm pump (a diaphragm pump can be used if it includes 100% stroke length to enable smooth dosing of the off-gassing liquid).

Off-gassing is when off-gassed liquid vapour has become entrapped in the pump, preventing it from pushing the liquid forward. This situation occurs when the pump is sitting idle or has low pumping rates, often at night, or when the pipes are exposed to heat, or any combination of these factors.

Peristaltic or magnetic-drive gear pumps can manage some level of off-gassing (especially when properly designed to handle air in the system and prime/perform a suction lift), but a vane pump has superior off-gassing capabilities.

Dry running

If your pumps could run dry, you really don’t want to consider progressive cavity or gear pumps. Rather choose a peristaltic, vane or even a diaphragm pump.

Leak-free operation

If leak-free operation is mandatory in your facility, especially if you’re handling hazardous materials, you can’t go wrong with a mag-drive pump, whether vane or gear. These pumps are used by many chemical manufacturers in ATEX rated zones, refineries, plants in remote locations because mag-drive pumps are known for their long-term performance and reliability.

As a second option, you could try a diaphragm or progressive cavity. A peristaltic pump can also be used to pump hazardous chemicals, but there is risk of damage to the hose, which increases maintenance requirements to avoid rupture or leakages.

Maintenance requirements

If you need a pump which doesn’t cost a lot to repair and doesn’t need much maintenance, you can consider the diaphragm pump. One small caveat is that it can be a little complex for a layman to fix – you might need to bring in a professional.

Other excellent choices for minimal maintenance include mag-drive pumps, either vane or gear. As mentioned, peristaltic pumps need regular maintenance due to wear to the hose. Meanwhile, progressive cavity pumps need somewhat regular maintenance, but maintenance can be complex and expensive, which adds to the overall workload.

Cost

If cost is your biggest consideration, it’s time to look at the cheapest of the metering pumps in our collection – the diaphragm pump. This is low cost, at low feed rates. Up to 500 LPH allows the lowest cost compared to other metering pump alternatives, but costs rise dramatically after 1000 LPH.

Other low-cost options include mag-drive pumps, while progressive cavity and peristaltic pumps have a higher capital cost. Due to the low maintenance requirements of PC and peristaltic pumps, this cost can be offset over the long-term, but it’s something to keep in mind when choosing the best option for your facility – and your budget.

So which pump makes the top of our best metering pumps selection?

Clearly, its impossible to choose the best metering pump without knowing what application it will be used for. However, peristaltic metering pumps are a good all rounder for most applications, due to their high practical flow and pressure range, good chemical compatibility and a host of other factors summarized in the chart below. However, if leak-free operation is crucial, you’d need to look at the mag-drive vane pump.

The below table sums up the main characteristics required by a metering pump, rating each metering pump according to its capabilities.

	Metering	Pumps	Comparison
			Magnetic Drive	Magnetic Drive	Progressive
	Diaphragm	Peristaltic	Gear	Sliding Vane	Cavity
Characteristic:
Practical Flow Range (max.)	1000 LPH*	30,000 LPH	4000 LPH	2200 LPH (900 LPH)	10,000 LPH
Practical Pressure Range (max.)	16 bar	16 bar*	10 bar	10 bar (6 bar)	20 bar
Chemical Compatibility	Excellent	Good	Excellent	Excellent	Poor/Good
Turndown Capability	Poor	Excellent	Good	Good	Good
Lack of Pulsation	Poor	Good	Excellent	Excellent	Excellent
Slurry/Solids Handling	Good	Excellent	Poor	Poor	Excellent
Viscosity Handling	Good	Excellent	Good	Good	Excellent
Off-Gas Handling	Poor	Excellent	Good	Excellent	Poor
Dry-Run Capability	Good	Excellent	Poor	Excellent	Poor
Leak-Free Operation	Good	Poor	Excellent	Excellent	Good
Maintenance Cost	Low	Medium	Medium	Medium	High
Maintenance Frequency	Low	High	Low	Low	Medium
Maintenance Complexity	Medium	Low/High	Low	Low	High
Capital Cost	$	$$$	$$	$$	$$$$

 

Ultimately, you need to look at all the above characteristics and see what metering pumps meet most of your needs. The above chart should really help you in choosing between these top metering pumps, but as always, if you have any questions, give us a call on 1-800-367-4180 (toll-free).

As your metering pumps supplier in Ontario, we’re here to help you choose, install, maintain, and monitor a variety of equipment. And to answer questions about things you’ve previously tried gone wrong.