‘In-series’ versus ‘in-parallel’ vacuum systems – which is best?

With Airflex Pro machines, you have a choice between ‘in-parallel’ or ‘in-series’ vacuum systems. But which is best?

‘In-series’ vacuum systems:

When two vacuum motors are positioned ‘in-series’, this means the motors are fitted in-line – with one motor pulling air through the exhaust of the other. Mounting the motors ‘in-series’ gives you higher waterlift, but lower airflow.

‘In parallel’ vacuum systems:

When vacuum motors are mounted ‘in-parallel’, this means the motors work independently, each pulling through air separately. Mounting the vacuum motors ‘in-parallel’ gives you double the airflow but lower water-lift.

What is water-lift?

Water-lift is a measurement for strength of vacuum. You may have seen the advert where the vacuum cleaner salesman picks up a heavy bowling ball using only the suction on a vacuum cleaner? Well, the higher the water-lift, the heavier the weight the suction can lift.

For this reason, with high water-lift the suction feels stronger if you put your hand over the end of the vacuum hose. When carpet cleaning, the wand is harder to push and pull.

High ‘water-lift’ is often used as a sales tool – because it seems obvious that the stronger the suction feels, the faster the carpet will dry…right? Not necessarily! Because there’s another very important vacuum reading to consider – Airflow.

What is airflow?

Airflow is the volume of air the vacuum system can move and how quickly it moves it. On professional carpet cleaning machines this is normally measured in CFM (cubic feet per minute).

In a simple experiment, a yellow ball is placed on the desk.  The vacuum hose is slowly lowered down towards the ball until the ball is sucked up to the hose:

The In-Parallel vacuum system lifts the ball from 3.5cm

The In-Parallel vacuum system lifts the ball from 3.5cm


The In-Series vacuum system cannot lift the ball from the same height

The In-Series vacuum system cannot lift the ball from the same height

So how does this relate to carpet cleaning performance?

In-series vacuum systems:

  • Suction feels stronger with hand placed over end of vacuum hose
  • Harder to push and pull wand on the carpet
  • Vacuum strength means you can pull larger volumes of heavy water – better for flood water recovery
  • Slower wand passes needed when extracting
  • Slower to reach full vacuum each time wand is placed down
  • Tendency for wand to ‘lock-down’ on carpet (which stifles airflow/water recovery)

In parallel vacuum systems:

  • Wand is moved more quickly
  • Very fast drying times possible
  • More responsive/quicker to reach full vacuum when wand is placed down
  • Easier to push and pull the wand
  • Performance can be significantly boosted by using 2” vacuum hose on longer hose runs

So which is best?

Most manufacturers of professional carpet cleaning machines have gradually switched over to airflow optimised ‘in-parallel’ vacuum systems. For example Century 400 (manufacturer of the Ninja machine) claim on their website that by switching from ‘in series’ to ‘in parallel’ (on their new Ninja Warrior machine), to have increased water recovery by an impressive 25%. We generally recommend vacuum motors mounted in parallel – for faster drying, faster cleaning and better performance on longer hose runs.

By | 2016-11-16T10:09:53+00:00 October 8th, 2015|Uncategorized|2 Comments


  1. Larry Cobb 21/08/2017 at 6:12 pm - Reply

    As a U.S. distributor for the Nijna Warrior when they brought it out, we were very disappointed in the performance.

    Our 1st customer had a Ninja Classic with dual 2-stage vacs in series. After buying the Ninja Warrior w/ 2st. vacs, he laughed at the vac performance and immediately returned the extractor.

    The Dual 3-stage warrior performed OK due to the higher lift of the vac motors.

    We believe LIFT is the most important vac motor spec.

  2. Matt @ Cleansmart 07/09/2017 at 10:53 am - Reply

    Thanks for posting Larry. We’re happy to supply our Airflex machines either in-series or in parallel, but in testing we found that the new 6.6 motors in parallel wipe the floor with the 5.7 motors in-series! You can move the wand about 3 x faster, drying is much faster and you can run very long hose runs and still have great performance at the wand.

    I used to use an old style Ninja every day for about 5 years. It’s a good machine and I know it very well, but the 6.6 parallel set-up is a massive step up. The maximum hose I would run from an old style Ninja would be 75ft (even at 75ft there would be a big drop in vac performance). There’s a video on of a customer using a 175ft hose run with the parallel set-up on this page http://www.cleansmartsupplies.co.uk/store/airflex-storm/#tab-reviews Maybe it’s to do with the difference in machine design also. Thanks anyway for your input, Matt

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