Fewer and simpler components in the company’s vacuum pumps is the result of ASF Thomas’ foray into DFMA design principles. Alan Quinn reports

Going back to first principles and looking at pump design from the ground up using DFMA (design for manufacture and assembly) was the starting point for ASF Thomas in developing its latest range of vacuum pumps.

Using the capabilities of three sites in the US, Germany and the UK, the goal of the development programme was to design a range of pumps which would lend themselves to fully automated assembly, or make more effective use of semi-automated production techniques or manual assembly methods.

Amongst the key areas explored were:

• How to design parts so that they cannot be assembled in any orientation except the correct one
• How to reduce the number of screws or eliminate them completely
• How to minimise the number of parts in any pump design.

A number of new production techniques emerged from the programme, including “snapper” technology, which allows products to be snapped together instead of requiring screws, nuts and bolts.

The first two products to emerge from the development programme were the LM22 and 5003 pumps. The 5003 emerged from the development of a pump specifically designed for a market-leading electrical appliance manufacturer. During a four-month development phase, ASF Thomas produced a pioneering membrane pump consisting of just eight parts and a single screw.

The pumps is assembled from its key elements – connecting rod, diaphragm, valves and gasket. The design of the drive bearing has been radically simplified also, and to ease assembly, the pump head is equipped with a tried and tested clip fastener.

In contrast, the LM22 was developed as a universal pump. It is a low noise design, intended for the widest range of applications which can be achieved at minimum cost. Fully adjustable without increasing pulsation, a vibration damping version is available and the design allows a DC version to be offered at minimal added cost. A low cost suspension has been developed, with a accessories including a connection manifold with integrated noise damper.

• ASF Thomas

October 1999

Hoerbiger-Origa has come up with a novel pneumatic valve that promises improved control and miniaturisation. Tommy Miller has been finding out

Following pioneering developments in piezo technology for pneumatic control, Hoerbiger-Origa (Interface) has made further advances in electro-pneumatic control. The new Megamic interface brings the benefits of silicon technology to the field of pneumatics and, in so doing, new levels of control and miniaturisation are now possible.

At the heart of the Megamic concept are Silicon electro-pneumatic micro-valves, which combine silicon technology with advanced actuation principles. With minute dimensions, low capacity electronic control and the highest degree of precision in a wide temperature range, the Megamic valves should be capable of fulfilling a variety of specialist applications.

Development of the actuation principle and construction of the Megamic silicon micro-valves were carried out in close co-operation with the Fraunhofer Institute and the Hahn-Schickard Institute for Micro and Information Technology.

The encapsulated silicon chip is actually a micro-valve, inside which a valve plate is moved by electrostatic attraction, and it is this that regulates the flow of gases. Various valve functions can be realised, such as 2/2 and 3/2-way valves, normally opened or closed. Electrostatic attraction allows the valve to be controlled with the smallest possible electrical current in a large temperature range.

Small amounts of air are regulated precisely, and this can be used for the full pressure range of pneumatic equipment, typically 0-16 bar. Additional components make this micro-valve more flexible for various flow rates and voltage ranges.

For automation technology, the micro-valve is combined with a pneumatic booster, resulting in a miniature valve only 10mm wide and with a nominal bore of 1.5mm. Given a suitable control circuit, the valve can be controlled with a TTL-peak signal. The miniature valve is ideally suited to miniature medical devices, analytical equipment, micro-assembly equipment and for piloting miniature conventional valves.

By utilising the silicon technology, further developments will enable the complete integration of sensors, control and communication electronics to facilitate the production of intelligent micro valves.

• Hoerbiger-Origa

October 1999

Advertising feature: The speed of a Festo Premier Stockist’s new cylinder delivery service is going to cause shock waves.

Festo Premier Stockists exclusively offer a SURCHARGE FREE same day and next day emergency breakdown manufacture service on ISO and VDMA cylinders on any stroke length from 8mm to 125mm bore.

Add to this access to over 40 cylinder types, and diameters from 2.5mm to 320mm, being in the Premier League means we can guarantee the fastest delivery across the widest range of cylinders in the UK.

You’ll find in most instances that when we talk days or even hours, our competitors are talking weeks.

You can rely on your local Festo Premier Stockist for a cylinder service with maximum velocity. 

Our cylinder service in action

Here is an example of an emergency where, without Festo’s impressive same day turnaround, the customer would have incurred huge downtime costs.

At 8.00am a fault is found on a main cylinder of a food packaging machine. Immediately a telephone call straight through to the local Festo Premier Stockist puts the frequently used process in motion. The stockist understands the problem straight away – it’s a non-standard stroke length, non-Festo cylinder that has failed. He recommends to the customer to use Festo and their unique surcharge free same day cylinder service for this emergency breakdown.

Stockist checks the availability of production kits using their ISDN direct electronic interface and communicates the urgent order to Festo. The essential information from the stockist is transmitted to the flexible small batch cylinder manufacturing cell. At 8.45am the CNC program is downloaded to the machine tools which are governed by the meticulous ISO 9002 specifications. The quality procedure demands build inspection at each stage of the assembly. The final test ensures the product’s integrity for its outstanding life expectancy of 10,000km of operation.

By 10.15am it is ready and a motorbike courier picks up the critical cylinder for the 200 mile journey to the customer’s factory. At 2.00pm stockist arrives at factory to ensure that all goes well and assists with the installation. The machine is back up and running, problem solved in just 6 hours and customer extremely satisfied. Festo aim to provide the fastest emergency cylinder service in the UK.

For more information contact:

• Festo Ltd,
  Automation House,
  Harvest Crescent,
  Ancells Business Park,
  Fleet, Hampshire
  GU13 8XP

• Tel: 01252 775000
• Fax: 01252 775001

November 1999

At last, a valve island that does not result in a compromise on either cost or performance. Tommy Miller takes a closer look

Few people would dispute the benefits to be gained from using valve islands: compact packaging, simplified wiring, and economical to install (compared with wiring and plumbing a multitude of discrete valves). However, it is seldom the case that a machine or item of equipment will be populated with pneumatic actuators that all require the same specification of valve.

In the past this has meant that the machine designer either has to compromise by fitting the valve whose flow rate corresponds to the maximum demanded by any of the actuators or, alternatively, fit valves that suit the majority of actuators but that might restrict the performance of one or more larger actuators. Of course, the designer could opt to fit discrete valves for the larger actuators, but this, as with the over-engineered option, rather defeats the object of using valve islands.

Many manufacturers of valves already give customers a choice of push-in connector sizes, and there is almost always a choice of valve configuration (5/2, 3/2, etc). But, until recently, it had not been possible to mix valve sizes within the valve island. This situation has now changed thanks to the introduction of the Multimach valve island by Metal Work.

Any number of valves from one to 24 can be used within the island, with flow rates for each covering a range of 150 to 800 Nl/min at 6bar, depending on the valve used and the size of the fitting selected; valves come in three sizes with widths of 11 and 14mm, and port diameters of 4, 6 and 8mm.

More user-benefits

But the list of features does not stop there. Electrical connections are made via a 9-pin or 25-pin connector and the valves have been designed to be easy to install and maintain. For example, the push-in fittings, valve-on indicator lights and manual overrides are all readily accessible with the valves in situ. A particularly useful option is for bistable overrides as an alternative to the usual spring-return type – very handy for commissioning and maintenance.

Multimach valve islands use a sandwich configuration, rather than a base of fixed length with add-on valves and blanks. Not only does the Multimach approach save space, but it also saves cost through avoiding the need to purchase an oversize base and a number of blanking units for mid-sized valve islands.

An extensive range of options is available to allow users to configure the islands with, for example, side-facing or rear-facing electrical connections, and air supplies at one end, both ends or with intermediate supplies too. And when it comes to the valves themselves, there are 5/2, 3/2 (normally open and normally closed), and 5/3 valves with closed centres.

• Metal Work

July 2000

How has turning a ball-and-socket joint back-to-front led to significant performance improvements in hydraulic pumps and motors?  Tommy Miller explains

Hydraulics is often perceived as an engineering discipline with plenty of rugged, dependable, powerful solutions for problems of motion or high loads, but little innovation. One type of product, however, has just benefited from some lateral thinking combined with up-to-date design and manufacturing methodologies.

Axial piston pumps and motors have been with us for many years and have proved to be particularly suitable for hydraulic transmissions; Linde started using such components in its fork lift trucks in the 1950s. But now the company has come up with a concept that results in pumps and motors that are more compact, have a higher power density, and are cost-effective.

At the heart of the new products is a design of piston and slipper pad that is the reverse of the norm: whereas the ball end of the ball-and-socket joint is usually on the piston and the socket is on the slipper pad, the New Generation Series 02 units have the ball on the slipper pad and the socket on the piston end. This may not sound like a leap forward, but the results speak for themselves.

One of the main advantages of this arrangement is that the swash angle may be increased from the normal 18deg to 21deg. For the same overall size of pump or motor, the swept volume is thus increased. And because fluid power is directly proportional to the displacement per revolution, the power density increases. A secondary benefit of this alternative arrangement is that the piston can now be hollow, which reduces the weight of the rotating components and improves lubrication.

From the outset, one of the objectives for the 02 pumps and motors was to use common parts for both types of product. This has indeed been achieved and the rotating groups – as well as many other components – are common to both. Other elements of the design have also been made modular so that even models of different capacity share common parts. The result of this approach is that Linde can streamline its manufacturing and reduce its stock holding, thereby making cost savings that can be passed on to customers.

Manufacturing technology

Additional investments in dedicated machine tools, automatic manufacturing systems and new machining techniques, together with improved materials specifications, have led to better surface finishes being achieved on the critical components. Running clearances between the dynamic components can therefore be reduced, so there are lower frictional losses, higher volumetric efficiencies and, consequently, an improved overall mechanical efficiency. There are four model ranges that benefit from the new developments: variable pumps for closed circuit operation; variable pumps for open circuit operation; fixed motors for open and closed circuit operation; and variable motors for open and closed circuit operation.

Linde claims that every type provides high performance, high efficiency and low noise, all from a compact, cost-effective package.

And for noise-sensitive environments, there is a special version of the variable pumps for open-circuit operation that feature an accumulator on the high pressure side. This acts as a silencer because it reduces pressure pulsations from 38.7bar to 11.3bar – which gives a useful 2 to 4dB(A) noise reduction.

• Linde Hydraulics

June 2000

Truck industry partnership results in unique power take-off selector valve

Working in partnership with leading European truck industry systems manufacturers, Parker Pneumatic has developed the new and unique, single unit PTO Selector Valve to control the engagement and disengagement of power take off (PTO) on commercial vehicles.

With the growth of heavy commercial vehicles such as mobile cranes, loaders and tankers, PTO plays an increasingly important role. Power take off is a truck industry term for an auxiliary gearbox which is driven through the vehicle’s main transmission to provide power to drive hydraulic pumps, fan blowers and other ancillary equipment.

Selection and deselection of the PTO function is a safety critical operation with the potential to cause injury to the operator and passers-by, or to cause expensive damage to the PTO or the main transmission system. Perfect manual interface with the control system is essential to achieve a safe interlock, eliminating the possibility of human error.

A common cause of damage and potential injury identified by Parker Pneumatic relates to PTO engagement, via a latching type of electrical switch, when the system remains operational until manually released. Deselection of the interlock via the release of a park brake or speed sensing unit selects a disengaged status for the PTO. If the operator or driver is unaware of this deselection, the next time the park brake is applied or speed is reduced, the PTO will try to engage, causing damage to the PTO or main transmission and possibly creating a potential hazard for passers-by.

As a leader in the development and manufacture of driveline controls for the heavy truck industry, Parker Pneumatic turned its attention to providing a solution to the problems of PTO control. Initial research in the UK and European truck markets identified the underlying requirements and the Parker team started on the development of the unique PTO Selector Valve, bringing to bear the group’s experience in the field of electro-pneumatic control.

Parker Pneumatic’s new PTO Selector Valve combines both electronic and pneumatic functions and incorporates important safety features for the protection of operator personnel, other road users and the general public, and to prevent mechanical damage to the PTO and drive chain.

The PTO Selector Valve provides a fail-safe interlock system designed to be applied to both stationary and/or moving vehicle power take off applications. The PTO Selector Valve also includes functions for signalling engine management systems, linking with an emergency stop and in-operation warning lights or audible klaxons.

Designed and built to IP68, the unit, connectors and cable are of non-corrosive materials to enable chassis mounting in the vicinity of the vehicle’s PTO, fulfilling an important requirement identified by bodybuilders. The electrical switch is of non-latching design, ensuring that in the case of automatic deselection of the interlock, further engagement of the PTO will not occur until manual reselection has taken place. The PTO Selector Valve incorporates a full interlock system, requiring only connection to the interlock source. For truck OEMs, this significantly reduces the number of relay and switch components to source, stock and install.

For further information contact

• Parker Hannifin – Pneumatic Division
• Walkmill Lane, Bridgtown, Cannock WS11 3LR
• Tel: 01543 456000
• Fax: 01543 456001

• Web:www.parker.com

October 1999

Norgren has produced an objective detailed and useful gide for OEMs and end users to explain the different types of pneumatic actuator and specify the right kind of actuator for each specific job.

For many applications cylinders can be allowed to run at their own natural maximum speed. This results in rapid mechanism movement and quick overall machine cycle times. However there will be applications where uncontrolled cylinder speed can give rise to shock fatigue noise and extra wear and tear to the machine components. This natural speed is determined by cylinder size port size inlet and exhaust valve flow air pressure bore and length of the hoses and the load against which the cylinder is working.

From this natural speed it is possible to either increase speed or as is more than often the requirement reduce it. The natural speed can be changed by valve selection: generally the smaller the selected valve the slower the cylinder movement. When selecting for a higher speed however the limiting factor will be the aperture in the cylinder ports. Valves with flow in excess of this limitation will give little or no improvement in cylinder speed.

The aperture in the cylinder ports is determined by the design. Robustly constructed cylinders will often be designed with full bore ports. This means that the most restrictive part of the flow path will be the pipe fitting. These cylinders are the type to specify for fast speed applications and would be used with a valve having at least the same size ports as the cylinder. Lighter duty designs particularly small bore sizes will have the port aperture much smaller than the port’s nominal thread size. This has the desired effect of limiting the speed of the cylinder to prevent it from self-destructing through repeated high velocity stroking. The maximum natural speed of these cylinders can often be achieved with a valve that is one or two sizes down from the cylinder port size.

Large bore cylinders are designed with port sizes large enough to allow fast maximum speeds. In many applications however they are required to operate at relatively low speeds. For an application like this a cylinder can be driven from a valve with smaller sized ports than those of the cylinder.

Once a cylinder/valve combination has been chosen and the load is known the natural maximum speed will be dependent on pressure. For an installed cylinder and load an experiment can be carried out. Connect a control valve that will cause the cylinder to self-reciprocate. Then start the system running at a low pressure and gradually increase it. The cylinder will cycle faster and faster until a limiting speed is reached. This is the optimum pressure for that application. Increase the pressure further and the cylinder starts to slow down. This is caused by too much air entering the cylinder entering on each stroke. More time is therefore taken to exhaust it and results in a slower cylinder speed.

With any fixed combination of valve cylinder pressure and load it is usually necessary to have adjustable control over the cylinder speed. This is effected with flow regulators and allows speed to be tuned to the application.

For the majority of applications best controllability results from unidirectional flow regulators fitted to restrict the flow our of the cylinder and allow free flow in. The regulator fitted to the front port controls the outstroke speed. Speed is regulated by controlling the flow of air to exhaust which maintains a higher back pressure. The higher the back pressure the more constant the velocity against variations in load friction and driving force. On the other side of the piston full power driving pressure is quickly reached. Many flow regulators are designed specifically for this convention.

• IMI Norgren
• Tel: 01543 414333

October 1998

A new series of air fuses from Norgren has spurred the launch of a companion CD-Rom, to help select which model from the 24 now available. But why an air fuse?

Anyone who has experienced the wild whiplash created by the free end of a severed tube or hose will appreciate the reasoning behind fitting an air fuse. Fitting this simple product between fixed or rigid pipework and flexible tube prevents the dangerous effects created by the loose end of an accidentally severed or uncoupled tube.

Air fuses work by shutting off the air supply when excessive flow occurs. During normal operation, air pressure on each side of the valve is about equal. The valve seat is held open by a spring, allowing unrestricted flow.

When a hose breaks, the air surge closes the valve. A small amount of air seeps through the side bleed hole. The valve remains closed as long as pressure on the upstream side is greater than pressure on the downstream side.

Unlike an electrical fuse, air fuses can be reset after the repair is made. The bleed allows air pressure to equalise on each side of the valve. When this occurs, the spring opens the valve and full flow is automatically restored.

Easy to fit to existing pneumatic systems, air fuses can make a major contribution towards a safer working environment, as well as helping to ensure that equipment complies with the Machinery Directive and PUWER (the Provision and Use of Work Equipment Regulations).

The air fuse should be installed directly between pipework, whether fixed or rigid, and flexible tube. Only tubing after the air fuse is protected. Failure to install the air fuse in the correct orientation will render it ineffective.

When a shut-off valve is located upstream of the fuse, the valve must be opened slowly in order to control the initial air flow, else the fuse could trip. For each port size, there are two types: a low shut-off flow type (0.14 bar drop pressure) and a high shut-off flow type (0.3 bar drop pressure). The port size should be nominally equal to that of the supply line: for example a 0.5in fuse should be used with a 0.5in ID hose. If there is sufficient system pressure for the length of hose to be protected, the high flow model should always be selected. If not, or where long hose lengths are to be protected, the low flow model is used. Each valve must be tested after installation to check it is functioning correctly.

Norgren’s new T60 series, a range of compact, tamper-proof air fuses for use in pneumatic systems, is available in a range of port sizes with pre-set shut-off flow rates, preventing anyone from tampering with the setting once it is fitted. It is suitable for use in industrial hand tool applications, such as blow guns.

However, with application variables such as inlet pressure, flow, length and diameter of tubing affecting which one of 24 different types of air fuse to choose, it is not surprising that some people find air fuse selection a confusing subject.

To help simplify the process, Norgren has developed an electronic package, in a spreadsheet format, which allows an engineer to input the specific criteria of a pneumatic system. It will then provide the optimum air fuse for that application. The software is available free in CD or floppy disc format.

Features of the T60 air fuse

tamper-proof design

compact and safe construction

low pressure drop

port sizes G1/4 to G1 half, available in high flow and low flow settings

high air pressure rating (maximum pressure 16 bar, depending on tubing specification)

automatic reset after failure correction – unlike an electrical fuse, it does not need to be replaced

high corrosion resistance

• IMI Norgren
• 01543 414333
• http://www.norgren.com< /a>