Positive displacement pumps vs gear pumps: which pump fits my needs?

True positive displacement technology is slowly but surely gaining ground on traditional gear pump systems for plural-component paint mixing in industrial finishing. Though promoted as the most suitable technology for years, gear pumps have a series of obvious flaws that can easily be solved by a PD proportioner.

SUMMARY

These are the benefits of true positive displacement at a glance:

Main drawbacks of gear pump systems

Although gear pumps work perfectly well for a variety of applications, they tend to be less reliable for plural-component mixing. Let’s look at some of the most common obstacles users face when working with gear pumps.

• Limited flow range
  A single gear pump’s flow range is limited to 80-450 cc/min. When flow rates outside this range are required, businesses are frequently forced to invest in a bulky and expensive setup involving multiple gear pumps.

• Industry standard mixing ratios
  Close tolerances between gears lead to material wear, particularly when solids or abrasives are used. Material slippage caused by worn-out gears reduces the accuracy of mixing ratios, which are often crucial in industrial finishing processes. Gear pumps typically operate within 5% accuracy in mixing plural-component material in factory paint mix rooms.

• Unsuitable for high pressure
  The maximum achievable pressure for gear pumps is 300 psi, which excludes a great number of industrial high-pressure applications.

• Slow reaction time
  When a gear pump stalls, it experiences creep loss and there is a delay while the pressure builds up again. To guarantee the correct pressure, operators need to be trained in timing and coordination of gun triggering.

• High maintenance cost
  Gear pumps contain several hard-to-reach parts that are generally expensive and difficult to repair and maintain. They often require total pump rebuilds, ranging in cost from €2,000 to €10,000.

• Limited compatibility with materials
  High viscous material packs between the gears, affecting flow and accuracy. Sometimes, chunks of paint come loose, clog the gun or end up on the part. Low viscous material leads to slippage in combination with wear on the gears.

• Sensitive to inlet pressure levels
  When the inlet pressure gets too high, gear pumps will sound the alarm and the entire line will shut down.

Positive displacement pumps

To achieve 100% positive displacement, industrial finishing systems are set up with dosing cylinder pumps or piston pumps. Positive displacement technology ensures better mixing efficiency, maximum flow control and consistent performance, while reducing solvent use and material waste. 

• Wide flow range
  There’s no need to invest in multiple pump systems for different flow rates, as positive displacement pumps can handle a wide range of flow rates using only one pump. A single PD pump system can typically offer a flow range between 20 and 800 cc/min[JB1] .

• Unbeatable accuracy
  Positive displacement technology manages to prevent material slippage and packing altogether, and it keeps a constant material flow. Because of these feats, it can achieve an exceptional mixing ratio accuracy: within 1%.

• Suitable for high pressure
  unlike gear pumps, PD pumps are perfectly capable of functioning in high-pressure applications, with pressures as high as 1,500 psi.

• Fast reaction time
  PD pumps can stall under pressure, which means that the system maintains the optimal pressure creep while it is not being used. When the operators are ready to resume their work, all they need to do is switch the system on and continue working.

• Low maintenance cost
  Maintenance and repair costs for PD pumps are very low, as they can easily be maintained and repaired in the field, and their parts are easily accessible.

• Compatible with most materials
  Positive displacement pumps are not sensitive to wear, and they are immune to material slippage and packing. They offer accurate and consistent results for high viscous and low viscous materials alike.

• Minimal impact from the inlet pressure
  The inlet pressure feed barely affects PD pumps. They have a 50% leeway regarding target inlet pressures, so there is no risk of the entire line shutting down.