A vane pump or rotary blower for wastewater vacuum trucks? It’s a question I have been toying around with for some time. There are appropriate uses and situations for each vacuum technology, but before I share my suction strategies, I should explain in detail how each machine works. 

A vane pump compresses air to create a void where vacuum is created. Depending on the model, it will take anywhere from 45 seconds to 2 minutes to build up vacuum to start working. A rotary blower displaces air to create that vacuum, creating negative pressure in seconds, and the technician is ready to work.

There are a few factors to consider either way to go. For example, the size of hoses you’re using and the size of your truck’s vacuum tank. 

Vane Example: If your vacuum tank is on a portable restroom service truck and you’re using 2-inch hoses, a rotary vane pump wouldn’t take very long to build vacuum and you can start working pretty quickly. But let’s say you have a 6,000-gallon tanker trailer with the same rotary vane pump. You’ll wait a few minutes to have the air vacuumed out of that tank before generating adequate vacuum to begin work. Also, let’s not forget that most of us backflush when we pump septic tanks. That means every time we have to reverse the truck and put the waste back into the septic tank to stir its contents, we have to switch the pump back into vacuum and build up vacuum again. You’re spending a lot of time building vacuum.   

Blower Example: Tiny restroom service trucks will have vacuum immediately. Using a blower, you’ll maybe save a few seconds, if any. But on that 6,000-gallon tanker trailer, you would have instant suction. No more waiting on the truck to build vacuum. During the backflush cycle — after putting the waste into the septic tank to stir it and putting the valve back into vacuum — we would have instant suction again to start pumping. I see this as offering a huge time savings.

CHOOSING A VANE PUMP

Rotary vane pumps are typically what we pumpers carry and have serviced. They usually offer trouble-free operation. They last 10 to 20 years. They do require turbine oil and the draining of mufflers daily. High use and high cubic feet per minute usually require a liquid cooling of the pump, while the smaller pumps are air-cooled.

Vanes in the pump rotate around a rotor. The rotor has two bearings that allow it to rotate with little to no friction. These pumps can range from creating a mild pump noise to becoming really loud. These pumps take power from the PTO, and the truck usually runs at 900 to 1300 rpms. So, noise will range with the specifications of the pump and truck.

Vanes aren’t too costly if they break, usually about $400 for the set. And they are replaced as needed. We’ve gone 13 years on a set, and they measure out near new. And if a prefilter fails and a rock gets in, the repair cost is about $100. We keep extras in our shop. The purchase cost of rotary vane pumps can range from $2,000 to about $6,000, depending on features and cubic feet per minute rating.  

The only two wear items on the rotary vane blower are the vanes themselves and the bearings. Special turbine oil is required to keep the pump operating. An oil catch following the pump collects the oil used during operation, and it must be drained daily or you’ll leave “oil blast” marks on your client’s driveway.

This pump is designed to “use/consume” oil. So the driver needs to keep the oil tank full and check the level often. We purchase our oil in 5-gallon buckets, and it runs about $95. With three trucks, including one backup rig, the bucket lasts us about a month. The waste oil collected out of the oil catches goes to an oil recycler after we’ve saved 100 gallons. 

GOING WITH A BLOWER

Rotary blowers — you may have heard them called “displacement blowers” — displace air to create their vacuum. I don’t have any of these yet, but in my research, I have found they don’t require any oil, and just like vane pumps, some have liquid cooling and some don’t. Displacement blowers require higher revolutions per minute, so a 2:1 gearbox will be needed so you don’t have to run your engine up so high.

In my research, I have found that displacement blowers are loud, and I mean very loud. In order to combat that, the manufacturers have enclosed pump features with exhaust silencers that have helped significantly. Blower maintenance costs are low. There is only one wear item, the bearings of the rotor. That’s not too bad. But they have an Achilles’ heel: overheating and liquids or debris contact. These are significantly more expensive to repair, and their down time is longer waiting for parts. Cost of a blower is usually $10,000 and up. 

OUR VACUUM PLANS

So what are we going to do at our shop? Well, we aren’t going to take down a perfectly good vane pump and replace it with a blower. Also, judging that we’ve never broke a vane or a vane pump, it’s going to be a long time before we replace a pump with a blower, if ever.  

Our plan is to purchase a newer truck in about a year and have a new blower placed on it. It will be great to see the difference in performance on the bigger trucks.  

On smaller septic or restroom trucks that don’t require extended time to build pressure, a vane pump remains a common choice. Most pumpers I have talked to about this continue to use vane pumps when they don’t have a special reason to go with a blower. They view blowers as more expensive at the outset and that breakdowns are more expensive to fix. Although I have to believe if I maintain my secondary and prefilters, I will be most happy with a blower on larger trucks and rotary vane pumps on the smaller trucks.