High-Impact Hand Tools

Soil compaction is an essential component in the construction
process. Increasing load capacity, preventing soil settlement,
hindering frost damage, providing stability, stopping swelling and
reducing water seepage, soil compaction is the art of increasing soil
density and optimizing soil stiffness on a construction project — and
it has numerous benefits.

On large jobsites, it’s the job of big ride-on rollers (those large
static or vibratory wheel compactors) and for smaller jobsites
vibratory plates and walk-behind padded or smooth drum rollers are the
name of the game. But when it comes to really confined compaction jobs,
a rammer is often the best solution.

rammer (also called a jumping jack) is one of the most popular handheld
compaction units on the construction site. It looks similar to a
jackhammer, but with a large flat shoe on the bottom instead of a
hammer bit. Rammers deliver high-impact, percussive force to the
ground, which is great for compacting cohesive and semi-cohesive soils
such as clays and silts. And while rammers are designed for cohesive
soils, these machines will even work on granular materials such as sand
and gravel. Rammers compact by discharging a flat shoe at high speeds
into the ground. Typically, two sets of alternative compressed springs
provide the acceleration forces, ramming at a frequency range between
500 to 750 blows per minute.

“To put it simply, it’s a giant foot that jumps up and down,” explains
Russell Warner, Ingersoll-Rand product marketing manager for concrete
and light compaction equipment. “But it’s not just the weight of the
rammer jumping up and down in the soil. When the foot is off the
ground, compressed springs release and cause the shoe to strike the
ground — that’s where the force comes in. To watch the rammer run, it
might appear that the machine is jumping up and down and the static
weight of the unit is what’s compacting the soil, but it actually
shoots that foot back down and creates impact force. That’s really the
key to compaction with a rammer.”

Rammers are key tools for utility and general contractors — especially
sewer, water main and gas crews, as well as plumbers. You can often
find contractors using rammers for backfilling foundations,
reinstatement around footings and general compaction during utility
installation, around manholes and in trenches. Anywhere there is a need
for a smaller, confined compaction machine for mainly cohesive
materials or higher clay content, a rammer is a great solution.

Today, there are a variety of manufacturers making rammers for the
compaction industry. BOMAG, Wacker, Ingersoll-Rand, MBW, MMD,
Multiquip, Sakai, Dynapac and Stone Construction Equipment are just a
few of the prominent brand names in the market. Besides brand, there
are a myriad of options in the rammer industry, including engine type,
shoe size, weight, dealer network, impact force, stroke and cost.
Finding the right rammer is about understanding your options.

“All rammers aren’t created equally,” says Peter Price, manager of
products and training at BOMAG’s Light Equipment Division. “When
contractors buy a [rammer], they mainly look at the shoe size and the
impact force. But other factors come into play, such as mass and
amplitude, which are just two of the factors that may differ from one
machine to the other. These factors will affect the productivity and
performance characteristics between the units.”

Getting into the Specs

Rammers today are evaluated on a variety of different specifications —
impact force, frequency, weight, stroke and engine power are all good
examples. Unfortunately, some of these specs can be hard to understand
and pin down. Take impact force for example, which is one of the most
popular and most difficult specifications to qualify for rammers.
Impact force is purportedly a measure of the energy produced by the
rammer when it strikes the ground. A high-impact force combined with a
high rate of blows per minute supposedly produces good compaction
results, but how impact force is measured is a bit of a puzzle — even
for manufacturers.

“Customers are looking for a number — how hard does the machine hit?”
says Frank Multerer, president of MBW. “Obviously, they want that for
comparative purposes. But the problem is that impact force is more
dependent on the deceleration values of soil at any given moment in
time than it is with anything having to do with the rammer itself. If
you assign a value to it, that value is by nature ephemeral. It changes
as the stiffness and the density of the soil changes during the process
of compaction. Impact force is not something that is dependent on the
rammer as much as the material that the rammer is striking.”

Many manufacturers will argue that the old Construction Industry
Manufacturers Association (CIMA) standards (“Uniform Method for Rating
Vibratory Rammers”) used for judging impact force do not equate to fair
numbers for comparative value. “Those standards were more of a windfall
for our marketing department than for any meaningful use in an
engineering sense,” says Multerer. The LEMB Standard No. 1 uses a Ball
Test Procedure to assess impact force, which is judged in pounds. Most
rammers today have an impact force between 3,000 and 5,000 lbs.

“The old CIMA standard was ok in its time,” says Price. “We as a
manufacturer will measure to the CIMA standard and the competition will
measure to the CIMA standard for the same machine and get totally
different results. There are so many influencing factors that affect
the CIMA standard test results of a rammer. So manufacturers have
collectively been working with ISO — the International Organization for
Standardization — to come up with an international testing standard
that is much more accurate.”

Until then, impact force may have the feeling of a
mystery number, yet many manufacturers still rely on it
to help judge a good rammer and sell their machines.

That same argument can be applied to another specification called
stroke. The stroke of the rammer is the height of the shoe when it
comes off the ground. If your rammer has a high stroke, you will have
higher impact force if combined with adequate weight of the machine,
argue many manufacturers. A rammer with a high stroke can get itself
out of loose and soft material, can hit harder and can help with better
travel. Most strokes are between 2 and 3.5 in. Many manufacturers will
align a high stroke with good productivity in a machine — although
others say it’s another marketing tool.

“At times, stroke is used as a selling feature,” says Warner. “But high
stroke does not necessarily translate into higher productivity. Other
factors such as blows per minute, shoe design, balance, ergonomics and
machine efficiency all contribute. A machine that has more stroke than
is needed is actually wasting motion and therefore less efficient.”

Of course, as a group, manufacturers go to great lengths and expense to
measure the performance of rammers. Whether the current standards are
good or not is debatable. It is much like fuel economy on an
automobile. Whether or not the measurement reflects what the consumer
actually sees can be debated, but all auto manufacturers measure in the
same manner, so the numbers can be compared while shopping.

Overall, users should realize most companies do make a quality rammer.
That rammer just needs to be used with solid compaction practice to
work to its potential. The single most important factor in the
compaction process is lift depth. For any rammer application, that
means restricting lift (or layers) to not more than 12 in. on granular
soils and not more than 6 to 9 in. of lift on essentially cohesive
soils. If users use good compaction protocol, they can utilize almost
any brand. And since most of today’s manufacturers make a quality
compacting rammer, models are often judged on their long-term
usability (things like weight, ease of use, maintenance, emissions,
travel and hand/arm vibrations).

Weight-wise, most rammers fall in the 100- to 200-lb range (the heavier
machines are typically the diesel-powered units). Rammer weight is
important for the compaction process and so is how that weight is
distributed. The position of the mass of the rammer and how that
dynamic mass is used in the stroke is important. A rammer should have a
good balance of mass and not be too heavy for hours of use or for easy

Smaller units (often
around 120 lbs) are considered light-duty rammers, which are popular
with cities and utilities — great for narrow and short trenches. Then
you jump up to the most popular size for general construction, which
would be around the 140-lb rammer mark. Above that, you’ve got a low
volume category of heavier machines (in the 165- to 200-lb range),
geared toward big compaction jobs in confined spots.

Hand/arm vibrations are another huge factor in judging a rammer.
Rammers are basically designed to destroy themselves from constant
impact work. Eventually those large numbers of impacts per minute are
felt by the operator (especially after an eight-hour shift). Rammers
are some of the industry’s worst offenders when it comes to hand-arm
vibration, which can lead to operator fatigue and even carpel tunnel

Most manufacturers today are
working to reduce the levels of hand/arm vibration. To truly evaluate
the weight and vibration of a unit, an operator will need to run a few
units. During the demo process, evaluate how soft the handles and shock
mounts are. Make sure the unit has low hand/arm vibration, but also
good travel.

“It’s a balancing act,” explains Warner. “The shock
mounts have to be softer and that affects your control. You still want
to be able to crawl out of a ditch with your rammer. You want to
advance it without pushing and you want to control it.”

Safety and ease of maintenance will also play into the purchasing
formula. For safety reasons, you will want the throttle where the
operator can get to it quickly and control it. The kill switch has to
be easily accessible as well, and the rammer must have a predictable
and effortless travel. The clutch should also be easy and handy to use,
so you can cut back on operating speed for safe and precise compaction.

When considering maintenance, parts support should be easy and
affordable. It’s always good to do some digging about maintenance
costs. What does an air filter cost vs. a recoil rope vs. a spark plug?
Does this model take any special filters or anything that’s out
of the ordinary? That’s when you see some of your maintenance costs
creep up.

Also, a quality rammer will need reliable components. Ask the dealer
about oil-lubricated rammer legs and nitrated spring cylinders.
Percussion springs on high-stroke rammers should have strong
characteristics, so you’re not replacing them every year. The quality
of the bearings used, the quality of the clutches and the quality of
the components in general should all be discussed.

What Are
Your Options?

Finding your ideal rammer will necessitate that you take the machine
out for a demo operation and grill your dealer. Finding your ideal
rammer will also include outfitting it with the right set of options
and accessories. Once you begin to shop around, you will find there are
two big decisions you will need to make before you pick a new rammer —
shoe size and engine type.

Most standard rammers come with an 11-in. shoe size, but there are a
variety of choices. Picking the right shoe size will depend on your
application and jobsite. If a contractor needs to do small utility
trenches, 4-, 6-, 7- and 9-in. shoes are available. For larger
applications, 13-in. shoes or wider are available. Contractors can also
buy extra shoes for different applications. An extra shoe purchase will
typically range from $100 to $400.

standard shoe size on the light rammer is 10 in. or maybe 11 in. It
will vary a little from manufacturer to manufacturer,” explains
Multerer. “On the mid-sized rammer, the shoe size is almost invariably
11 in. As you move into the larger rammers, they can either be
purchased with an 11-in. shoe or as wide as 13- or 14-in. shoe and
sometimes as large as 15 in.”

with shoe size, buyers will also need to consider what type of engine
they want on their rammers. Today, there are five choices of engines —
2 cycle (gas/oil mix), 4 cycle (gas), diesel, electric and pneumatic
(air-powered). The most popular choice today is 4-cycle gas engines,
which have pretty much replaced the old standard 2-cycle engines.

“The latest versions of 4-cycle engines have allowed us to have
high-impact force and high stroke, but with the environmentally
friendly advantages of a 4-cycle engine,” says Price. “You burn less
gas, you don’t have to mix oil into the gas to lubricate the engine and
it has longer running times because you have more efficient fuel.”

The only manufacturer still making 2-cycle engines today is Wacker,
with its three models — BS 50-2i, BS 60-2i and BS 70-2i. Of course
Wacker still sells many more 2 cycles than 4 cycle rammers (four
to one, according to Mark Conrardy, sales engineering manager), with
price being identical for both engine units. In fact, Wacker is one of
the only North American OEM manufacturers still making 2 cycle engines,
and the company says it touts a lot of advantages.

“The spin you’ll hear from other manufacturers is that they’ve gone to
4 cycle because it’s so much better, but the reality is they don’t have
any other option,” explains Conrardy, noting Wacker does not sell its
engine to competitors. “The big advantages of 2 cycle is it’s actually
a simpler engine and there are fewer moving parts. Two-cycle engines
are designed to be very sturdy, while 4 cycles have a lot of parts and
they’re a little bigger as well, so you get a lot of stress on
components. The 2 cycles withstand that impact and shock better. And
what many customers forget is that when a 4-cycle rammer is out on a
long-term job, the oil in the crankcase needs to be changed every 100
hours. Who is doing that maintenance?”

Besides traditional engines, some manufacturers even make air-powered
rammers like MBW, with its model 450A. Like electric rammers, pneumatic
units are spark-free and have low decibel levels. It’s a niche product
for cities and gas companies where they are wary of explosion hazards
or noise.

Diesel engines are also
available today, but are not too popular, according to the
manufacturers CE spoke with. Diesel engines make the rammer much more
expensive (often in the $5,000 range) and much heavier (sometimes more
than 200 lbs). Wacker and Multiquip make good diesel engine units for
the rammer industry, but again they are niche products.

“There’s really two types of contractors that would use the diesel,”
says Warner. “The contractor that wants a common fuel source. They
drive up to a jobsite with a big tanker truck and their job is to fuel
every piece of equipment on that jobsite. It’s the backhoes, the
dozers, the skid steers — they’re all diesel. And traditionally,
there’s one little rammer that’s a 2 cycle or just straight gas, and
that’s a pain. So having a diesel rammer eliminates that problem. Then
there’s also the refineries. With a piece of equipment in a refinery
environment, they generally don’t like spark plugs so diesel is
preferred there.”


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