Efficient hydraulic components of the future can save energy

PK GuhaBy P.K. Guha, PMI International

The topics of energy conservation and alternate sources of energy have been buzzing around since I graduated from college in the mid-60s. The level of excitement vacillates depending upon how Arabian and/or OPEC nations are interfacing with the Western developed countries.

In 1970, I hosted Dr. Narr, who was investigation the opportunities of the abundant wind culture around the coast of the Indian ocean, in collaboration with the Government of India under the chairman of Kesub Mahindra, of Mahindra & Mahindra, the Industrial giant in India. We agreed that energy saving through efficient products is essential—and of equal importance to searching for alternate sources.

It does not matter really how the energy is generated and where it comes from, as long as it is clean and economical—and efficiently used.

This is where “efficiency” comes into the picture. How efficiently we can produce the energy from a variety of sources, as well as how efficiently we are using the energy. We generate energy various sources: Wind, sun, water, coal, nuclear and petroleum. The important factor is that we had better learn to use energy intelligently, through efficient products.

The fluid power industry is one of the largest consumers of energy across the globe. Whether we are digging earth, making bricks or producing steel, hydraulic products are used everywhere. This is where fluid power products and applications have immense responsibility. We need to design and produce the most efficient products that consume less and less input power. Hydraulic products generally can be divided into two broad categories, dynamic and non dynamic.

Dynamic products
Dynamic products are those that have dynamism inside due to rotating components: Pumps and motors. The cylinders and directional/servo/proportional valves also comes under this category to some extent.

The volumetric efficiency of the pump or motor will determine how efficiently they are in using the input energy. Today, most pump manufacturers (vane, piston, gear, screw, etc.) produce pumps that are 85 to 90% efficient. Rarely, a few can may reach 91 to 92%.

Presuming that a given pump is rated for 10 gpm at 100 psi and 1200 rpm, at 90% volumetric efficiency, the pump will provide 9 gpm at a maximum designed pressure of 3000 psi, while running at the same 1200 rpm. That means input energy was provided for 10 gpm but at highest pressure only 90% (9 gpm) of the flow is put to actual use. For the other 10% of flow, which is lost internally due to internal slippage, input energy used for it also wasted, without any actual work done.

This obviously is the wastage of input energy. The cumulative loss of millions of such pumps running around the globe, in a variety of applications, seem insurmountable. If we can save some of this lost energy, that would be as good as producing it from any regular or alternate source of energy production.

The same phenomenon applies to a hydraulic motor. The output rpm and torque produced by a hydraulic motors, if not in commensurate (1:1 ratio) to input flow with certain pressure applied to the motor inlet, then the input energy drawn by the pump is further wasted.

The big question for the designers and hydraulic engineers is, how can we make 100% efficient pumps? Is it possible? Internal slippage in pumps and motors is simply part of the design—some amount is needed to lubricate the mating components. So how can we reduce the internal slippage, and thereby make the given pump close to 100% efficient.

These are the questions we will have to answered in the years ahead. There are many ways that future pumps could be designed with close to 100% volumetric efficiency. The cumulative effect of the saving will be humongous.

Non dynamic products
Non dynamic hydraulic products have fewer moving components inside, and have more of a static nature. These products are not running continuously during the equipment duty cycle. All varieties of pressure control, flow control, directional control, check and other types of hydraulic valves are examples. They do not have many mating components, and internal slippage is not as much of an issue here.

Many of the control valves are of open and close type, along with sliding spool valves. Particularly for the sliding spool valves, a certain amount of internal slippage is required to maintain a microscopic film between the spool diameter and the body bore.

Therefore, energy loss in way of internal slippage is a concern with the hydraulic valves too. However, with the hydraulic valves the energy that we lose is due to the pressure drop across the valve inlet and outlet.

The cumulative losses in millions of valves in thousands of machines—and in all applications globally—are enormous. We are talking about multi-Megawatts of energy squandered.

Here again, lot has been done by major manufacturers to improve the pressure drop phenomenon in a valve. However, more improvements are needed to be achieved in the future, to make the valves more and more efficient to save energy.

Some of the key factors for these improvements could be:

• Different metallurgical compositions for the casting
• Sliding/gliding flow pattern through the valves
• Finding a way to reduce resistance to the flow inside the valve
• Improved surface finish of inside machined platforms

Among the non dynamic products in a hydraulic system, there are number of accessories which creates resistance to flow unnecessarily to create heat. This is a source for loss of energy.

Currently, many hydraulic application/circuit designers are mindful to calculate out the BTHU losses per cycle of machine operation. Then they provide an adequate heat exchange/xooler to dissipate the created heat. In other words, we are allowing the system to generate heat and then cooling it down to safeguard the fluid and some other components. So we lose energy in the first place and instead of finding out a remedy, we pay extra to cool it down! That is kind of like burning currency.

With more efficient pumps, motors, valves and accessories, a well-designed hydraulic system may not even need a cooler or heat exchanger, as we will not lose much of energy in the way of heat. That is the future we should be looking for.

Lastly, heat losses (energy) through the hydraulic pipes, hoses and manifold blocks are insurmountable, no matter how much better cooling system we provide. Moreover, putting cooling system is not a solution to saving energy in anyway.

Heat loss due to the pressure drop phenomenon in hydraulic pipes and hoses cannot be totally overcome. Therefore, we have to find a way to reduce the fluid travel resistance in the steel pipes, hoses and blocks, and keep it to a bare minimum.

Here are a few thoughts on efficient process of fluid conveying in hydraulic system to save energy:

• All right angles inside a Manifold block should be rounded
• Improve polishing of hydraulic tube’s internal diameter
• Reduce pressure drop across the strainer, filters and diffusers, through using better ultra-thin paper technologies
• Above all, find better lubricating additives for the hydraulic fluid

Product development in the fluid power industry has come a long way. Over the last 50 years, enormous advancement in design and manufacturing of hydraulic pumps, motors and valves have taken place. There are wide varieties and types of pumps, motors, valves and other controls now available in the global market for an entirely new generation of applications. Many of these products are 1960- or 1970-era designs, but are still very popular today.

We are at a threshold where we need new innovation in hydraulic pump and motor design and technology, to improve efficiency. With the U.S. being the leader in many technology developments, the new innovations may have to come from us. Ane new innovations naturally create better jobs, too.

The new innovations have to come from academic engineering institutions as well as from privately funded R&D programs.

China, with all its growth, is still a developing country. Whatever fluid power products are designed and manufactured in Europe and in the U.S., practically overnight the replica is available in China, at half the cost and in “will work” conditions. And none of these Chinese hydraulic products are made to original engineering specifications.

Volumetric efficiency and envelope size
The improvements in question are the volumetric efficienct and envelope size of hydraulic pumps, motors and valves. Indeed, over the years, a lot of modifications have been made, when we compare the sizes of old Vickers PVA 120/150 pumps vs. the current Rexroth A10V 100 size. What a difference! However, the volumetric efficiency has not significantly changed to save energy.

The overall industry in the globe is moving faster towards unknown technological achievements. Twenty years back, most around the world did not know about the internet; now we cannot live without it. Fifteen years ago, cell phones were only available to a few. Today, it seems everyone has a cell phone, if not two. It’s a necessity, then luxury, for day to day living. Not too long ago, 35 mm cameras were our best source of photography. Today, digital cameras with limitless features are very common and inexpensive.

The design of fluid power products must catch up with other industry trends and keep pace with machinery and equipment design and developments.

Where do we go from here?
Faster, quicker and energy conservation will be the buzz words in the industry that we will live in the future. It already is!

The volumetric efficiency of most vane, gear and piston pumps produced today ranges between 89-91% and in very specific cases may be 92%. In every pump produced today, 8 to 9% of the mechanical energy is converted to heat energy. This correspondingly reduces the productivity of the machine or equipment, where it is being used—not to mention the cost of the energy losses!

Just imagine, there are more than 10 million pumps in operation around the world in all kinds of applications. If volumetric efficiency of each pump is improved to at least 95% from 85-90%, there will be 5-10% less heat loss, which is energy saved. Multiply that by 10 million pumps, and it’s an enormous amount of BTU saving. This would be as good as installing few windmills and producing a whole lot of photovoltaic solar panels. What an effect it will have on the environment!

How could this be achieved?
Understandably, 100% volumetric efficiency cannot be achieved in any hydraulic pump or a motor. As explained earlier, there must be certain amount of internal slippage allowed in every pump to lubricate the internal dynamic components. How, then, can we work around this? The internal slippage in a hydraulic pump and motor is the result of clearance and tolerances between various mating components. Designers have to focus on how best can we tighten these clearances and tolerances, to reduce the internal slippage, as well maintain proper lubricity. Here are few possible clues:

In a vane pump:
• Clearance between the vane thickness and rotor slot width
• Clearance between cam ring and rotor thickness/height
• Timing groove improvement in pressure/wear/flex plates
• Timing groove improvement in the inlet/outlet kidney pocket area
• Reduced vane tip loading
• Metallurgical improvement
• Improved surface finish in mating components
• Better and newer lubricating additives in the hydraulic fluid

In a piston pump:
• Piston diameter and cylinder block bore clearances and surface finish
• Increased pre-load force between the valve plate and cylinder block face
• Redesigned timing notches on the face/wafer/valve plates and cylinder blocks
• Positioning of valve plate kidney pockets
• Metallurgy and heat treatment improvements

The key to the better volumetric efficiency is to reduce the internal slippage source. There are legitimate obstacles in tightening few of the clearances. However, many of the current popular vane or piston pumps on the market today are such old designs that the clearances and tolerances provided for each components and assembly are based on the then machining capability in the industry. Today, through CNC/digital machining technology, a high degree of close machining tolerances and clearances—as well as surface finishing—could be achieved for every component, much more easily then before.

Imagine the impact of saving in all the following industry, where millions of pumps, motor and valves are in constant operation: The newly designed pumps and motors with at least 1% increase in volumetric efficiency alone would save an insurmountable about of energy, equivalent to building several nuclear power plants.

Industries and applications
Automotive/bus & truck: Power steering, transmission
Lawn & garden: Hydrostatic transmissions
Steel mills: Rolling, Tube testing furnace operation, coiling, stripping, testing
Construction/agriculture: Loaders, dozers, cranes, backhoes, skidders, dumpers, tippers, tunnel borings, tractors, combines
Food processing: Conveyors, material handling, canning
Forestry: Feller benchers, log cutting, stripping, shaping
Road building: Pavers, finishers, steam rollers, and related equipments
Railroad: Tie tampers, ballast consolidators, rail layers, diesel locomotives
Mining: Drillers, roof supports, conveyers
Material handling: Utility vehicles, wood choppers, forklifts
Machine tool/metalworking: All varieties of metal forming, cutting, shaping, milling, grinding, planning, die casting, boring, presses
Rubber: Presses, curing, auguring
Offshore drilling/oil & gas: Variety of related applications, with the drilling process
Packaging: Presses, balers
Plastics: Injection, Blow molding of variety of kinds
Pulp & paper: Slurry auguring, conveyors, calendars and tension adjusters
Power generation: Coal ash remover in thermal generation and other different kinds of material handling
Textile: Weaving, spinning, calendering
Windpower: Braking, blade profile, maintenance and direct generation
Marine: Fishing trawlers, ship application, under water cameras
Aviation: Variety of applications in all kind of aircraft and aircraft ground testing applications; airport ground control equipment
Spacecraft: Shuttle and rocket positioning vehicles

From the above, one can imagine that there are unlimited boundary of hydraulic applications, hydraulic pumps, motor and valves. Therefore, even a minute 1% volumetric efficiency improvement will be as good as setting up few additional energy production plants, be it conventional or the alternate source.

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