EPA shows off hydraulic hybrid technology.

Cramming liquid into tanks and squirting it back out again doesn't sound like much of a high-tech attack on global warming and the energy crisis.

Or does it?

"This could be one of the most important advances in automotive technology--ever," Charles Gray Jr., director of the Environmental Protection Agency's Advanced Technology Division, said during a presentation at Manchester Boston Regional Airport.

Gray and a host of other officials were standing outside the regional UPS facility to show off a demonstration UPS truck that uses "hydraulic hybrid" technology to boost mileage by a whopping 70 percent, compared to about 30 percent for current hybrid engines.

The truck is similar to hybrid cars such as the Toyota Prius, except it stores energy inside 22-gallon tanks of compressed liquid rather than inside an electric battery. This sounds clumsy, but the EPA says it is much more efficient in a big, heavy vehicle that makes lots of starts and stops--like a UPS truck--as well as being cheaper to build and fix.

"There's nothing here that a mechanic can't look at and say, 'Oh, I see,'" said Robert Varney, regional administrator of EPA's New England office, who has been driving a Prius since he moved up to the federal job in 2001, after a dozen years as New Hampshire's environmental services commissioner.

EPA's lab in Ann Arbor, Mich., has put the hydraulic hybrid technology in a dune buggy, a Ford Expedition and a pickup truck, where they studied its use as a "power boost" launch system. Engineers have tackled questions both prosaic (what fittings resist leaking the best?) and deep (how to manage the relatively low energy density of hydraulics).

EPA has been working on hydraulic hybrids for about 15 years, Gray said, at a total estimated cost of about $60 million in federal money, plus lots of industry assistance.

"If we were an industrial research lab, we would have spent a billion dollars," said Gray, pointing out that Toyota's electric-hybrid research has easily spent that much.

The UPS truck, which came to Manchester as part of a national tour, is the first working real-world prototype of the technology, with hopes of reaching production stage in a few years.

Gray said the technology is drawing enormous interest from auto firms such as Ford and Toyota.

It's obvious why UPS, which burns tanker-loads of diesel daily in more than 90,000 delivery vehicles, would be interested.

The EPA says it expects that in a heavily used vehicle like a UPS truck, the roughly $7,000 cost of the technology could be recouped in less than three years, through lower diesel and maintenance costs.

"This can make the economics work, and work quickly," said U.S. Rep. Jeb Bradley, who showed up at the presentation to take the truck for a drive around the parking lot, and also get a pat on the back from Varney for being a big supporter of the project.

There are secondary benefits for UPS, too. Like a Prius, the hydraulic hybrid can turn the internal combustion engine off and on instantly, a great benefit to a delivery truck that spends hours a day idling, and can even drive with the engine off, although only for relatively short distances. That means the company could operate the trucks inside its huge shipping warehouses without choking workers with exhaust fumes.

Hydraulics, which use the pressure of liquid squeezed through tubes to move things, have been part of cars from the beginning. They are best known in hydraulic brakes, in which the force of the driver's foot on a pedal pushes liquid through tubes until it presses against brake pads.

The hydraulic hybrid uses pumps called accumulators to compress hydraulic fluid to 5,000 pounds per square inch--future models will go twice as high, said Gray--and move it where needed, such as the real drive pump motor, which converts the pressure into rotating power for the wheels.

Much of the benefit of the technology comes from the fact that it recovers energy used in braking and releases it for more power. The Prius does the same thing, but hydraulics do it more efficiently, Gray said.

Another major advantage is that the hydraulic hybrid is a so-called series hybrid, rather than the parallel hybrid design of the Prius. This means there is no mechanical connection between the engine and the drive wheels basically, hydraulic fluid replaces the drive shaft--which allows much more efficient control of the motor.

Hydraulic hybrids are no panacea, of course. While hydraulics can store and release energy much more quickly than electric batteries if a cell phone was powered by hydraulics, it could be recharged in just a few seconds--the total amount of energy they can store in a given volume is much less.

That's why hydraulic hybrids can travel only a few hundred yards without the motor on, compared to many miles for a Prius.

There are also design questions about storing that much fluid in a vehicle smaller than a big truck.

For a big, heavy vehicle that makes lots of stops and starts and frequently idles, however, it could be ideal. So, while it may be a long time before a hydraulic hybrid car can be parked in your driveway, the technology might show up inside school buses or garbage trucks.--DAVID BROOKS THE TELEGRAPH