Rubble, dust, rocks – work at the Leibfritz gravel quarry in the Swabian Jura is anything but clean. Man and machine are subjected to extreme conditions here. A challenge for everyone – but above all for the filters used in vehicles and machines. Filter technology is put to the test every day.

A visit to the Leibfritz gravel quarry is not for the faint-hearted. The countryside of the plateau of the Swabian Jura is indeed tempting. Württemberg's "Fairytale Castle" Lichtenstein lies not too far from here. But this is anything but a fairytale. Thick clouds of dust hover over the 20 hectares of land, constantly swirling due to the heavy trucks moving around, transporting the grit, sand, and gravel out of the quarry. Managing Director Jürgen Werres, sporting dark blue dungarees, stubble, and a small earring – a real grafter – laughs as he gets to the point: "This isn't an office, plain and simple. It's a gravel quarry, a working mine. It's a tough job, working here."

A challenge for man and machine – and for the filters of MANN+HUMMEL that are used in almost all the heavy vehicles here.

Heavy vehicle

The quarry uses several heavy vehicles, including three semi trucks and four six-wheelers. They transport the grit, sand, and gravel that is used mainly for road construction. Werres leads the family operation, now in its fourth generation, together with Kurt Leibfritz. His great-grandfather founded the quarry in the 1920s. The company has been excavating Jurassic limestone since 1926. "Leibfritz gravel is a high-quality gravel with a good reputation. It is particularly pure and contains almost no impurities," says the Managing Director.

A tour through the gravel quarry and the mine is bumpy and dusty. Werres follows a dump truck in his own car. "It's carrying a cool 45 tons of material. It's almost certainly fitted with two-thirds MANN-FILTER products."

Since the start of the 1990s, the gravel quarry has used only filters from MANN+HUMMEL wherever possible. And the Managing Director makes no secret of this: "With new vehicles you can't do anything in the first two years because of the warranty. But afterward, we only use MANN-FILTER – be it a fuel filter, air filter, or cabin air filter. I have never had any complaints. In fact, we've never had problems like engine damage or blocked fuel lines," says Werres, praising the filters.

Special relationship with technology

Jürgen Werres knows what he's talking about. The trained mechanic began his apprenticeship at 15 years of age, after spending many years repairing lorries and trucks in his spare time. He didn't join the company until the age of 25, though. He was out exploring the world before that. In Saudi Arabia, he carried out maintenance and repair work for a haulage company's vehicles. He then traveled through Europe for two years – from North Africa to England, and Portugal to Hungary, all in a truck. Nowhere was too far for the native of Swabia, Germany.  

Since then, he has had a quite special relationship with vehicles and their inner workings. He almost goes into raptures when the subject of oil-bath air filters comes up: "It was an amazing invention. They're still in use in the desert today. It's a filter that never breaks. And more importantly, anyone can maintain one. Rinse with gas. Fit it back into the engine. Done. It worked." He proudly emphasizes: "We still have two vehicles with working filters. One of them is right here in the workshop."

Profile Filtration

Earth-moving equipment needs robust and high-performance filter systems. The following are just some of the MANN-FILTER used in the gravel quarry.

  • Air filters stop grime, pollen, and fine dust particles in the surrounding air from getting into the engine.
  • Oil filters permanently circulate the oil, filtering it for particles of dirt and combustion residue.
  • Fuel filters stop the particles and water in the fuel from damaging the engine.
  • Cabin air filters offer almost 100 percent protection against undesired particles and hazardous fumes.

Longer lifetime

The extreme strain placed on the vehicles means an increased need for maintenance. The Leibfritz gravel quarry does most of this work itself. A large workshop and several mechanics are on hand for repairs and maintenance. A lot of maintenance takes place in the winter when excavations in the quarry are hard-going. "It is very important to regularly maintain the machines and check whether we need to replace any parts. But it's a quick process – we call up the dealer and, within two or three hours, sometimes a day, we have the replacement part ready for installation. It is all very easy. If it weren't, the consequences could be fatal. A payloader engine costs over €80,000 and a filter costs €90. You can buy loads of filters for that kind of engine."

By saying this he means, the quality of the filters is also reflected in the longer lifetime of the machines in the gravel quarry. As recently as the 1970s, a truck had to be serviced every 4,500 miles, a figure that increased to 7,500 in the 1980s. Today, trucks can run 30,000 to 60,000 miles before the filter and the oil have to be replaced.

Brute force

It is the machines in the gravel quarry – wheel loaders, wheel excavators and drills – that come under a lot more pressure than the vehicles. "Because we work in a gravel quarry, that means we work with force, brute force. We use dynamite. We drill into the rock," says Werres. The weather conditions play a part, too. Temperatures can drop to -13 °F in winter. In summer, on the other hand, temperatures can sometimes reach up to 113 °F.

"Man and machine are really put under pressure here. If we get three hot weeks in a row in summer, then you won't find a single spot anywhere on the site that isn't dusty," says Werres.

In his car, he drives onto a hill where a large payloader is in action. In the cab sits Rosario Giobbe, cigarette in mouth, visibly concentrating. He never takes a break. "What do I do? Lift stuff. The dirt needs to go so that I can get to the rock face where the good stuff is. This is real hardcore work. Not everyone's up to the task. It depends on the technique. You have to use lots of techniques to ensure a full load." Giobbe knows what he's doing – others need a bit more training first: "There are plenty of people who simply drive over the heap, put the tires actually on it, but they can't fill the bucket properly," says the pro.

He plans to work another 1.5 hours. "Then I'll get in there with the drill. I've already drilled some holes up the top. You can see the dust, the debris." One drill bit weighs around 220 pounds and measures 13 feet in length. The permitted drill depth is over 100 feet. Giobbe sits in a cab while drilling. He never comes into contact with the dust – thanks to the cabin air filter of MANN+HUMMEL.

"There's lots of dust when you're drilling, though. And the drier it gets, the worse it is. That filters really have a job to do," says Managing Director Werres. The machine has two air filters: a cabin air filter and an engine air filter. These are replaced twice a year. If they aren't, the whole machine is at stake – a machine that costs three-quarters of a million euros, by the way.

"I'm assuming the good MANN+HUMMEL filters are in this one?" Werres asks his employee. He knows: "Yeah, those are from MANN+HUMMEL. They'd have to be, otherwise you'd look like a ghost."


Detonations are carried out on average twice a week at the Leibfritz gravel quarry. Around 4,000 tons are excavated per detonation.


Dynamite is used for blasting after the drilling is complete. Rosario Giobbe rings the alarm. With the first sound, the area is cleared and the workers take shelter. With the second sound, the charges are detonated. There is a bang, and the vapor from the dynamite spreads across a wide area. A third alarm signals that the coast is clear. After the blasting, dump trucks transport the large rocks (measuring up to 4 feet in length) to a primary crusher so that they can be broken down. The material is then collected in a large buffer silo.

Giobbe is about to start his sixth year of work at the Leibfritz gravel quarry. He originally trained to be an industrial mechanic, but he is also a master of dynamite. Hence his particular attachment to the machines – particularly the drill: "This is my baby. I never let anyone else play with it. I actually have a special relationship with all the machines. Starting with the car that I drive to the site. I always say that I treat the machines as if they were my own."

Witnessing history

The area being detonated today used to be a sea during the Jurassic period, around 200 to 150 million years ago. It is incidentally the reason for the many surprises on site – in the most literal sense of the word – such as any time a hole opens up after a detonation.

"When you are the first person to ever enter an area, you get this special feeling. Breathing the air there is just indescribable. You wonder when this happened and how much water it took to wash away all the chalk over the years," explains Jürgen Werres. Sometimes, age-old artifacts come to light in the form of fossils. Amateur geologists even found the fossilized remains of a squid once. But that's not to say you won't also meet living animals in the quarry. Lizards, frogs, foxes, and wild boar can all be found here.

Werres even has an appropriate anecdote ready: "I was walking around the site one evening checking the ground for the tires. Suddenly I heard a bang – it was a wild boar! It fell off the cliff and was lying about 30 feet away from me. I was completely shocked."

Swabian Jura: A region rich in rocks

The Swabian Jura traverses South Germany. The deposits of Black, Brown and White Jura rock can be traced back to a time when the region was still covered with water. Around 150 million years ago, in the White Jurassic period, a tropical sea with coral reefs, cycads, and ginkgo trees covered the area. Today, it is occupied by lime gravel that is excavated for the construction industry, and limestone that is used as a raw material in the cement industry. The layers of Jura ridge are made up of cemented sea mud and countless bits of housing. Such an abundance of limestone encouraged people to find a whole variety of uses over the centuries. This is why large stone quarries still shape the landscape of the region today.

Concentrating on the job

Right in the middle of the gravel quarry is where Werres appears to be in his element. If there's more material to transport than usual or if there's a manpower shortage, he's more than happy to step up to the plate himself. You'll always find him behind the wheel of a dump truck or working on a payloader at the dump. "You work every day and give it your best," says Werres. "If something's broken in the morning, it'll be repaired before you know it." Of course, he never takes his eye off his business. "The aim is to achieve the best results with as little material as possible. You have to be able to see that you have earned something. That you're not just standing still."

Focus here is directed completely on the job. The best example of this is Thomas Schrag, now known to everyone only as "Jumpes". He loads dump trucks with his wheel loader. These trucks, loaded with 40 to 60 tons of detonated and excavated material, drive through the quarry to the primary crusher up to 65 times a day. "Jumpes" has been at the gravel quarry for 35 years. Werres has this to say about him: "He's a specialist, and he knows the whole operation inside out. Even I have to ask him questions now and then." Schrag himself is more modest: "Ah, I don't like to gossip." "Yeah, he just likes to work," says Werres with a grin.

Even the Managing Director, it seems, has nothing else on his mind. When asked about the 90th birthday of the family company in 2016, he appeared somewhat stumped: "90 years, really? We haven't really given it much thought. We'll have to have a chat and find out what we're doing." But that's just what they're like at Leibfritz – more about "doing" than just chatting.

Working in a team with 15 well-rehearsed colleagues is particularly enjoyable here. Everyone can rely on one another. And everyone here is a pro in one way or another – the employees are commercial vehicle mechanics, carpenters, truck drivers, masons, drill engineers, or dynamite experts. The team of Horst Klotz and Sabine Ott takes care of telephone and written communication in the office. One thing is clear for Jürgen Werres: "Team spirit is very important. Everyone has their duties and everyone knows what they have to do. But if someone can't work in a team, it's like getting sand in the transmission. But it works for us, I have no complaints in that regard. The team is 100 percent behind me. And I am 100 percent behind my team. As it should be." 100 percent reliability is just as important as the job itself. The same goes for the technology that is pushed to its limits here every day.

Gravel quarry, Leibfritz - A 90-year tradition of stone

The Leibfritz gravel quarry was founded in 1926 by Martin Leibfritz in Sonnenbühl-Undingen where the gravel manufacturing operation ran until 1964. Since it was no longer possible to extend mining rights after this time, the company switched to excavating and selling Jura limestone material in Lichtenstein-Unterhausen in the year 1964. The family company is currently in its 4th generation and is managed by Jürgen Werres and Kurt Leibfritz. It supplies customers within a 20-mile radius.

But the work doesn't stop there. "We deliver rocks and sand to the Frankfurt Zoo. They set up an enclosure there which they want to mimic a desert. Our yellow sand was ideal," explains Jürgen Werres. The customer is one of Werres' favorite topics: "We live for our customers. We couldn't sell anything without them. If you're nice to the customer, you'll get the same treatment in return. If you are reliable and punctual, if the quality is good enough, the customer will come back." Werres also believes it is important to maintain contact with smaller customers, be they landscape architects in Raststatt, or a builder just round the corner who comes by to buy a few rocks for his fountain.

Hard work: the filters need to provide top performance at Leibfritz gravel quarry.
Jürgen Werres: "Team spirit is very important. But it works for us, I have no complaints in that regard. The team is 100% behind me. And I am 100% behind my team. As it should be."
Jürgen Werres is keeping files to hand for an overview
A look at the dusty engine block shows exactly what the filter will be faced with.
Jürgen Werres initially discusses the repeat order of filters with Thomas Schrag.

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