Positive Displacement Blower for Insulation Machines

Positive Displacement Blowers (hereafter PD) are probably known better by their common name – Roots Blower. In the 1860s, the Roots brothers in Indiana invented this blower for blast furnaces. This blower is actually a pump. Unlike conventional insulation blowers which move air by using vanes, the positive displacement blower has two sets of lobes which do not allow any air to bypass. Thus, you get no loss of air volume.

Interview with Dave Krendl about the PD Blower.

Barry: Why should you have the upgrade to a Positive Displacement Blower?

Dave: There are three reasons why the PD blower offers advantages to the contractor that the previous double blower (centrifugal blower) does not offer.

  1. Long Distances: The first advantage is that the PD blower is like an air pump. When you are pumping long distances, there is no de-rating of the volume of air coming out of the end of the hose. When you are using a centrifugal system, you have to de-rate them about 10% every 50 feet. So, if you are putting out 100 CFM at the machine, you are only putting out 60-65% at the end of 150′ of hose.
  2. No Slippage of Air: You are losing air volume because the fan is actually slipping in the air stream because it has to push harder. With the PD blower, it is an air pump. With every revolution of the rotary lobes, you have the same amount of air out the other end. Therefore, when you are pushing long distances, high elevations or you are pushing a wet, dense, heavy product, your PD blower will perform better over those long distances.
  3. The Longevity of the Wear Life of the Unit. The PD blowers have a 10+ life span whereas the centrifugal blower has a life span of 1-2 years. So instead of replacing the blowers every year or two and dealing with the wear issue of the brushes, the PD blower will give you along term lifespan if maintained properly.

Barry: If a contractor is in the commercial applications with glue or adding water to cellulose, the PD blower is definitely a step up and will produce a finer blow.

Dave: Absolutely. Especially if you are going over 150 feet of hose, that PD blower will give you a much better consistent feed without any de-rating (or fall-off). Even if you have partial plugging in your hose, it pushes it through with much more intensity than the centrifugal blowers. The other application where a PD blower works well is if you are using an internal wetting system, the PD blower is recommended. If you are using it for fireproofing applications where you use a Rockwool with a Portland cement in it, the PD blowers perform much better.

Description of the set up of a Positive Displacement blower in the Cool Machines.

A positive displacement system involves more than just replacing the centrifugal blowers with a positive displacement pump. You need to order your machine with it from the factory. Here are all of the components:

  • Front Panel Box: wired for 240 volt. Has one dial for precision tuning of the air flow
  • 5 horsepower electric motor
  • Pump installed with piping
  • Rear Panel Box: Also contains a dial for tuning air flow. The pressure gauge is on the rear of these machines, so this secondary dial allows for precision dense-pack adjusting.
  • Large Round Air filter box which can be piped through the floor of your truck or trailer

Front Panel Box

Front View

Back View

Maintaining a Positive Displacement Blower

Air Cleaner
Inspect. If somewhat dusty, then use an air hose to blow out from the inside to outside.

If the dust is substantial and will not blow off easily, then replace with a standard air filter available at your local automotive store


Inspect Belt
Again, we use a standard V-belt. Inspect for cracks, debris and wear. In the 1960s, it was standard practice to spray belt dressings. These actually compromise the life of your belt. They soften the belt and will attract dust and foreign objects. They may temporarily eliminate squeaks, but that masks the problem. Squeaks indicate your belt is burned. You are simply spraying lubrication on a failing belt.Belts are not difficult to change and are inexpensive. If it squeaks, why not just change it? A new belt will prevent costly, time-consuming breakdowns on a job site.


PD pump oil case
There are two plugs on the PD blower (outlined in yellow). Remove both plugs. Add oil until it starts to seep out the bottom drain plug. You are not trying to fill the entire case.


Video Describing the Positive Displacement Blower