Gear Pumps for Metering Applications vs Diaphragm Pumps?

Metering or dosing refers to the delivery of an accurately measured amount of liquid. Metering, in one form or another, is used throughout all industries — from paper making to film processing, to chemical manufacturing, to plating, cleaning, etc.

Until recently, many users have considered only diaphragm pumps or piston pumps for their metering applications. Advances in electronics and process control solutions over the last 15 years, however, have closed the gap between rotary and diaphragm pumps, making metering with gear pumps a very simple and extremely accurate solution. Today, the traditional reasons for selecting a diaphragm pump over a gear pump are no longer valid. Typically, gear pumps can compete directly with diaphragm metering pumps up thru 10-15 bar.

Metering Pump Situations

There are three basic metering situations:

(a) Metering at a constant flow rate over a range of differential pressure;

(b) Delivering a metered flow in a set proportion to a process variable for the purpose of controlling the process variable (e.g., keeping a pH level constant);

(c) Delivering a given volume of fluid irrespective of flow rate – Batch processes (e.g., filling a tank to a specified level or volume).

Diaphragm and piston pumps historically have been associated with the first of the above metering situations, because of the following characteristics they possess:

• Precise volumetric displacement
• “Infinitely” adjustable range
• Pressure “stiffness” (i.e., the ability of a pump to maintain consistent flow rate over a wide pressure range)

Gear Pump Advantages in Metering Applications

Diaphragm metering pumps also can and do employ the same closed-loop technology that enables gear pumps to meter. However, in the final analysis, gear pumps can provide accurate and repeatable flow rates within the same general range of diaphragm metering pumps, and they offer the following advantages:

1. Virtually no pulsations – This allows flows to be easily and accurately measured with standard flow meters. Pipe diameters can be much smaller in relation to those used with pulsing diaphragm pumps whose pipe diameters are based on high instantaneous flow rates.
2. Lower NPSH requirements Gear pumps – require less NPSH because of their steady non-pulsating flow characteristics. Diaphragm or piston style pumps require higher NPSH because of their pulsations. (NPSH available decreases further as the viscosity of the fluid increases.)
3. Simplicity of design – Gear pumps are extremely simple to understand and maintain. There are no check valves to clog or fail, and no pulsation dampeners need to be placed in the line.
4. Multiple seal arrangements or mag-drives – Rotary gear pumps are available with single- mechanical seals, double-mechanical seals or seal-less mag-drives. There are no diaphragms to rupture, allowing process fluid to leak or destroy the pump, or gear box lubrication oil to enter the process that is being controlled.
5. Accurately controlled flow – With standard instrumentation such as flow meters, pH sensors, and variable speed drives, accuracies of +/- 0.5% are easily achievable.
6. Ease of automation – With off-the-shelf electronics such as variable speed motors, flow meters and pH sensors with standard 4-20 mA analog outputs, configuring a gear pump for a metering application becomes a very simple process.
7. Low cost – With the price of electronics being a fraction of what it was just 10 years ago, the cost to automate and maintain more efficient rotary gear pumps has decreased significantly. Metering using gear pumps is now considered to be one of the most cost-efficient methods of metering in industry today.

Why Liquiflo ?

For more than 35 years, Liquiflo has manufactured High-Alloy Gear Pumps, specifically designed to meet the demanding needs of the chemical processing industry. Liquiflo Gear Pumps handle flows from 0.1 to 55 GPM and differential pressures up to 350 PSI.  Liquiflo will custom engineer special pumps to suit your specific needs.

Gear Pumps and Centrifugal Pumps, specifically designed to meet the demanding needs of the chemical industry.  Liquiflo pumps are made from high-alloy materials such as 316 Stainless Steel, Alloy-C, Alloy-20 and Titanium.  By offering a large selection of corrosion-resistant internal materials and multiple sealing options – such as mechanical seals and magnetic-drives – Liquiflo pumps are capable of pumping a wide range of chemicals – including acids, caustics, solvents and polymers – over a wide range of conditions.

Gear pumps are self-priming positive displacement pumps that produce a non-pulsating flow and require lower NPSH (net positive suction head) to operate. They are ideal for metering applications and for pumping nonabrasive, viscous liquids at high differential pressures.  Liquiflo has extended the useful range of gear pumps into low-viscosity fluids by using a wide variety of non-metallic, self-lubricating and wear-resistant components. Liquiflo gear pumps have handled thousands of difficult chemicals and have been successfully applied in many difficult pumping situations, including high-viscosity, high-pressure and high-temperature applications.

Liquiflo gear pumps are a popular alternative to other pumping technologies, such as Diaphragm pumps, Progressive Cavity pumps, Peristaltic pumps and Piston metering pumps.  Gear pumps are an alternative to Diaphragm pumps because they do not pulse or require an expensive air source to operate. For metering applications, they do not require pulsation dampeners or other ancillary equipment. In continuous duty applications, they generally last longer than Diaphragm, Progressive Cavity or Peristaltic pumps, which require frequent part replacement, such as diaphragms, stators, rotors or hoses. Gear pumps have a simple principle of operation which makes them easy to understand and repair.

Liquiflo offers a large selection of standard pumps, kits, parts, options and accessories, which are available for immediate delivery. In addition, Liquiflo can customize pumps to meet your specific needs.

Our experienced application engineers, customer service representatives and worldwide network of distributors are available to assist you with your special chemical pumping applications.