Can Your Little Shop-Vac Suck Rocks Up?

The ability of a shop vacuum to suck rocks up is one of the most overlooked attributes of these marvelous tools.  Even small Shop-Vacs, with minor changes to their hose length, can have impressive pickup rates that compare to larger contractor grade vacuums.

 

Suck Up Rocks
Shop Vacuums have the capacity to suck rocks up.

Can Your Little Shop-Vac Suck Rocks Up?

by Titus Nelson, PE

Inventor of the Holey-Moley Digger

Does Your Shop-Vac Suck Rocks? Most people don’t even consider the possibility of sucking up rocks with their shop vacuum. The Shop Vacuum, one of the most under utilized tools in a garage, can do all sorts of marvelous things from blowing up air beds, to sucking out the gunk in shower drains. However, a big oversight is the incredible capacity of a shop vacuum to suck up rocks.

When I speak of rocks, I’m talking about gravel up to 2-½ inches in diameter. The noisy stuff; gravel that will give you the impression that your shop vacuum is about to break apart at any second type of rock. If you want to wake up your teen, make sure you get one of those shop vacuums with a stainless steel drum, it will sound like you just installed a megawatt boom box audio system in your car.  All silliness aside, shop vacuums are made for this type of stuff and they do a very good job of picking up gravel and the noise really isn’t that bad.  You won’t need any ear protection anyway.

So why do we care if a shop vacuum can suck rocks up?

When a shop vacuum can suck rocks up they can be used to dig holes.  Digging holes with a shop vacuum, while not a novel idea, is a very effective way to save your back and prevent sore muscles from repetitious use of hand tools. If you have a shallow hole to dig, or sand or gravel to move, especially if it is located in a place where it is hard to manipulate hand tools, a shop vacuum may be the right tool for you. If you haven’t used a shop vacuum for this unique task before here are a few things you need to know.

1. Filters – use a filter

There are many microbes in the soil and you will be breathing a lot of dust if you are not using a filter. A good HEPA filter or the new wet/dry washable plastic filters will significantly reduce the dust in the air.

Filters will get clogged relatively fast when vacuuming up dirt which slows down the dirt uptake process, so periodically turning off the vacuum, removing the lid and banging the filter a few times on the side of the vacuum drum.  This will knock off most of the dirt. This is where a simple face mask will come in handy.

You will need to empty the shop vacuum of soil before it gets too heavy, so this is a good time to bang the filter on the side of the vacuum container to loosen up the dirt building up. For dirt that is more resistant, or slightly moist, you may have to remove the filter to bang the dirt out. Most shop vacuums come with a diverter at the end of the hose where a bag is connected. This will divert the dirt down about 45 degrees and protects the filter. If the digging speed slows down, clean the filter.

2. Hoses – larger diameter & shorter length is better

Hoses for shop vacuums are typically sized to optimize the system performance. Vacuum cleaners will typically pull an 80% vacuum when completely shut off at the suction end; however, this rapidly drops off, as the end is opened to the atmosphere. For moving dirt, air flow rate is the key and the larger diameter hoses work better as they can take in larger rocks, and they have less restriction to air flow.  For most conditions 2 inch to 2-½ inch hoses work best for picking up dirt, sand, and gravel.  Many Shop-Vac’s have inlets that will adapt to 2-½ hoses that are available at most hardware stores.

The shorter the hose length the better for picking up rocks.  In tests we have seen nearly a doubling of gravel pickup rate when we reduced the hose length from 7 feet to 3 feet.  Make up a hose that is the minimum length that suits your needs.

3. Weight – gravel weighs a lot

To give you a comparison of weight, a gallon of water weighs 8 pounds.  A gallon of loose dry dirt weighs 10 pounds and wet gravel comes in at nearly 17 pounds per gallon. Soil weight adds up fast and only a few gallons becomes difficult to move. A ten-gallon shop vacuum filled with wet gravel can weigh in at close to 170 lbs and will be a bear to handle. As a rule of thumb, roughly 2 to 3 gallons of soil is within the realm of easy lifting and dumping.  You do not need a big shop vacuum for picking up rocks.  However, you will need bigger wheels and a handle for moving the dirt around, so a larger vacuum should be considered.

The following table lists the density and weight per gallon of various soils for reference:

Material Density (lb/ft3) Wt (lb/gal)
Dirt, loose dry 76 10.16
Dirt, loose moist 78 10.43
Loam 80 10.69
Sand, dry 97 12.97
Clay, dry 100 13.37
Clay, wet 110 14.70
Gravel, dry 105 14.04
Sand, wet 119 15.91
Gravel, Wet 125 16.71

The photo below shows a 5 gallon bucket with a test mixture of sand and gravel that weighs right at 60 pounds. Moving this bucket is difficult and raises the risk of injury to hands and back.   As a rule of thumb limit the amount of gravel to several gallons. Sucking up several gallons of gravel and dumping the contents into a wheelbarrow makes it much easier to move.  If you are going to pick up 5 to 10 gallons of gravel and move it with the shop vacuum, you will want to have strong wheels and a sturdy handle.

dsc_1034-1200x800-web

 

4. Wheels and Handle – the larger and sturdier the better

Digging holes is normally done outdoors in the garden on dirt pathways or around lawns where the typical shop vacuum small caster wheels will not work well. Small wheels and excessive weight make them useless for moving dirt from one location to another. When digging holes with shop vacuums with small wheels, it is best to empty the container into a wheelbarrow for transporting. However, a number of shop vacuums, usually listed as Contractor, Professional, or Industrial models, have large rear wheels and a handle. These will usually manage 100 to 200 pounds of weight and can be moved over dirt or lawns without too much difficulty. These professional models typically have 12-amp ratings and larger hoses in the 2 inch to 2-1/2 inch range.

 

Ridgid WD19650 Shop Vacuum
Ridgid WD19650 Shop Vacuum

 

When digging with your shop vacuum, you can use any of a variety of tools to loosen up the soil and then vacuum up the loose soil direct with the vacuum hose. If you are removing the soil to plant, some of the soil may be put back into the hole.  By dumping the soil out on a tarp next to the hole will work well for mixing it with planting soil. You will find that the soil in the shop vacuum will have a very fine consistency.  You can easily separate the fine soil from rocks and heavy gravel with a screen. A pea gravel screen on top of a wheelbarrow also works well for this task.

https://cat6tools.com/rectangular-hole-soil-volume-calculator/
Sand, Clay, Gravel removed from hole and separated with a screen

5. Shop Vacuum Rating – higher airflow rating the better

Most shop vacuums will vacuum up dirt, however one attribute of a shop vacuum that stands out over everything else for picking up dirt is flow rate.  Flow rate is generally listed in (CFM) – Cubic Feet per Minute of airflow. This is usually measured at the vacuum inlet without any restriction. The greater the CFM rating of the shop vacuum the better. In addition, shop vacuums with 180 to 200 CFM ratings are super for digging holes. Many shop vacuums will show or list horsepower.  This is quite misleading as it is usually determined in a laboratory.  The horsepower is at at stall speed of the motor which never happens. A better way to look at power is to look at watts.

The wattage rating can be found by looking at the amp rating of the vacuum cleaner. The largest shop vacuums are usually rated at 12 amps. Volts x amps = watts and the voltage is assumed to be 120 volts.  The amp rating is more than adequate for comparing shop vacuums. A good rule of thumb is the higher the amp rating the more power the vacuum has for digging. A shop vacuum with a 12-amp rating, a flow rate of 180 to 200 CFM, and a 2 to 2-½ inch hose should be more than adequate for digging.  When shopping for a shop vacuum, you may see two 6.5 hp vacuums that look alike. However, one will have a 12 amp rating and the other an 11-amp rating.  So make sure you are getting the higher amp rating.

5. Most shop vacuums will do the job

The four shop vacuums below will all pick up gravel.   Note the hose adapter openings. These are all suitable for 2-½ inch hoses. Number one is a Ridgid 16-gallon with a rating 12 amps.  Number two is a 14-gallon Shop-Vac with a rating of 12 amps. Both are contractor or commercial grade.  Number three is a 6-gallon Shop-Vac with a rating of 8 amps. Number four is a 5-gallon Dayton with a rating of 6 amps.  These four vacuums were tested for the amount of time to pick up 15 pounds of gravel.  All of them work well for digging.  Finally, number four, the Dayton was pulling over 100 CFM picking up 15 pounds of gravel,  This was half the rate the Ridgid at 208 CFM.      In conclusion, the four shop vacuums sucked up gravel at 0.3 to 0.7 pounds per second.  See the chart below.   These are impressive rates.

 

Does your shop-vac suck rocks?
Four shop vacuums tested for their capacity to pick up gravel

 

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6. Improving Performance – use the shortest hose possible

The best fix to improve the performance of a shop vacuum is to shorten the hose length.  When shortening a hose from 6 feet to 3 feet, all shop vacuum pickup rates increase by 100% or more.   The smaller shop vacuums, had dramatic increases in pickup rate, especially the Dayton with an increase of 150%.  In addition, the Dayton, with a 3 foot hose exceeded the pickup rate of the Ridgid with a 6 foot hose.  However, the Ridgid had a phenomenal pick up rate of 1.36 pounds of gravel a second.

Conclusion

All shop vacuums can suck rocks up.   A shop vacuum needs to be beefy to carry more than a few gallons of heavy gravel.  At a pound per second pickup rate,  it takes seconds to pick up enough to be hard to lift.  Finally, reducing hose length by half will improve the ability of any shop vacuum to suck rock up by 100%.

 

People who liked this article like these products:

 

Portable Engine Driven Shop Vacuum System

https://cat6tools.com/product/shop-vac-assisted/

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