Bosch 4 Gallon Hand Carry Compressor

Great fit and finish and good air volumn make this a reliable shop or job site compressor


Bosch 4 Gallon Hand Carry Compressor

Bosch Tools has recently entered the pneumatic tool market with five new compressors and seven new nailers. Three of the compressors are of the 'hand carry' style, perhaps a more apt description than 'portable', as the other two models are of a wheelbarrow style, which makes them just as portable.
The Bosch CET4-20 is a twin tank 4 gallon medium-sized compressor, about the same size as other twin stacks on the market. What's unique about Bosch's design is that the tanks are vertically oriented (upright and at a slight angle). This design has a number of advantages. First, it makes the CET4-20 surprisingly easy to move to and from the truck, even considering its 73 lb weight. While there is a handle on the top of the CET4-20 (which you can use for short distance moves), I found it much easier to carry the compressor close to my body, grasping onto the roll cage. Second, and not surprisingly, this design makes it much more efficient for the moisture in the tanks to drain to the bottom, where, as you would expect, the drain valve is located. And third, the vertical design means that the CET4-20 occupies less floor space than a horizontal design.  
The controls are housed on a recessed panel in between the tanks. The recessed panel means that the controls are better protected against workplace mishaps, yet easy to access. The tank and outlet pressure gauges are large and easy to read, and the pressure regulator big enough to pull and turn even with chunky work gloves on. The safety release valve is up high as well, on the top, backside of one of the tanks. I see a lot of guys pull the valve at the end of a work day to release air pressure in the tank, rather than venting pressure from the drain valve. The purpose of the safety valve is to prevent failures by automatically relieving pressure when compressed air reaches a predetermined level.

Controls are large and easy to read
Roll cage protects the motor, pump and various switches
A sturdy roll cage gives a fair degree of protection to the innards - motor, pump, power switch, safety release and check valves, and air filter. Nonetheless, the filter on my compressor arrived broken. I was mildly surprised that it had a plastic housing, but realized that this was likely because the filter is considered a 'consumable' item. The filter prevents dirt and debris from compromising motor performance or durability. It needs to be inspected on a regular basis, and replaced as necessary. Large rubber feet add stability to the compressor and reduce vibration (and perhaps have some sound dampening effect).

Top handle for short distance moves
Conventional power switch
The CET4-20 has a neat 'EZ Drain' system; a drain valve that enables both tanks to be drained from the front of the compressor. This is much more convenient than having to reach behind, and tilt up a horizontal twin tank compressor to access the drain valve. To avoid rust build-up in the tanks, make a habit of draining them at the end of each work day.

Safety release valve is easy to access
Plastic air filter - metal would be preferable
A 2 HP single stage 2-pole induction motor drives this compressor, delivering 4.2 cfm of air at 100 psi. This is enough air volume and sufficient pressure to run just about any air tool I've a mind to use, except possibly a sander. The smaller horsepower motor runs cooler than a higher HP motor, meaning less wear and tear on engine parts, and less noise. The CET4-20 uses a contractor grade oil-lubricated pump. You can expect a longer work life over an oil-free model. It does require more user-maintenance; you need to check the oil level regularly, topping it up when low.
A conventional oil dipstick lets you know exactly how much oil is left in the tank, so it's always clear when it's time to add more. Of course it would be more convenient if there was a sight glass on the pump so you could tell with a quick glance how much oil was in the tank. Every six months or so, you should replace the oil in the pump; if you use the compressor on a daily basis change the oil more frequently. Along with having to be diligent with checking the oil level, you shouldn't place an oil-lubricated compressor on an incline of more than about 10% as the piston won't dip into the oil reservoir. You might also find it harder to start in colder environments. There is a stiff steel tray on the bottom of the CET4-20 that adds a further level of protection to the motor and pump.

EZ Drain valve works very well
Large rubber feet add stability and reduce vibration
All compressors have a duty-cycle rating. This refers to the actual pump run time per hour compared to the off time per hour expressed as a percentage. This translates into how much time you can operate a compressor in a given period of time. Most portable compressors run at a 50% cycle, which means that the compressor pump should run not more than 30 minutes out of every hour. Otherwise, the pump will have to work too hard, which will cause overheating and will drastically reduce its work life. For finish carpenters, cabinet installers, furniture makers and the like, who typically use their compressors on an intermittent basis, this shouldn't pose a problem. Tradespeople, and production shops that rely heavily on compressors for such tasks as sanding or grinding will likely select a large upright compressor with an 80% or 100% duty cycle anyway.

Oil dipstick
A steel plate at the base of the compressor protects the motor and pump
The compressor comes filled with oil. All you need to do is 'break it in' before using it. This involves running the compressor for 20 minutes with the drain valve open. A pretty simple procedure that is clearly detailed in the instruction manual. When you first start the compressor it takes about 45 seconds for the tanks to fill. Thereafter, the tanks recover in about 10 seconds, which is pretty darn fast (and less irritating on the ears). I filled the tanks, turned the compressor off, and then let it sit all night. The compressor didn't loose a single drop of air. In the shop the CET4-20 isn't overly loud. I measured the noise level at 83 dB. It's been on a job site twice, with both an 18 gauge brad nailer and 23 gauge pin nailer connected. No complaints at all.
So far, I'm happy with the performance of the CET4-20. The fit and finish on this compressor are superb. It gives me all the air I need to run my nailers, has a great 10 second recovery time, is reasonably quiet, has the best tank drain system around, and is easy enough to cart back to the truck at the end of the day. At just under $450 it's priced a bit higher than other twin stacks on the market, and it only offers a 1 year warranty. Still, unless it conks out unexpectedly, I feel that it's good value for the investment.


  • 7 3/4" W by 19 3/4" H by 16 1/4" L
  • 4 gallon tank capacity
  • 2 HP single stage 2-pole induction motor
  • 4.2 cfm @ 100 psi
  • Oil lubricated pump
  • 10 second recovery time
  • EZ Drain system
  • Roll cage
  • 72.7 pound weight
  • 1 year warranty

Manufacturer:Bosch Tools
Available From:Search for your local retailer
Retail Price:$449.00
Model #:CET4-20
Made In:China
 Carl Duguay, August 2010
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