Energy Savings with Pneumatics

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113/10/2011 | Phil O'Neill, Bosch Rexroth Pneumatics | © Bosch Rexroth AG 2011. All rights reserved, also regarding any disposal, exploitation, reproduction, editing, distribution, as well as in the event of applications for industrial property rights.

Fluid Power ExpoPhil O’Neill

Bosch Rexroth PneumaticsCleveland, OH

10/26/2011

Global Trends Reduce costs

Consider total cost of ownership- Not just acquisition costs

Increase efficiency Improve throughput Reduce cycle times Minimise waste Reduce power consumption

Environmental awareness Carbon emissions

Has to have a short payback period

So what’s the problem ?

Pneumatics has a bad name Inefficiency

Inefficient design by rule of thumb- Using higher pressures than necessary- Using higher wattage coils than necessary- Oversized valves- Oversized actuators- Not minimizing pressure drops

- Long tube runs- Undersized tubes

Leakage Poor connections Worn seals

Why do we care ?

Because it’s expensive More expensive than it needs to be

Where’s the problem ? After all, air is free !!

Compressed air isn’t free. One of the most expensive energy storage media

What does it cost to run your compressor ? There is a need for a TCO balance

Operating costs (approx. 70%) Initial investment (30%)

- Acquisition cost- Installation & commissioning- Maintenance

How big is the problem ? Source - www.energystar.gov “Leaks are a significant source of wasted energy in a compressed

air system, often wasting as much as 20-30% of the compressor’s output.

Compressed air leaks can also contribute to problems with system operations, including: Fluctuating system pressure, which can cause air tools and other

air-operated equipment to function less efficiently, possibly affecting production

Excess compressor capacity, resulting in higher than necessary costs

Decreased service life and increased maintenance of supply equipment (including the compressor package) due to unnecessary cycling and increased run time.”

Google “Compressed air leak”

What can we do about it ? Establish a baseline Measure air consumption at no-load

Leakage How to measure leakage ?

- Hearing ?- More sophisticated ?

- Totalising mass flow meters- Measure overall leakage

- Ultrasonic leak detectors- Locate leak points

Quantify the cost That gets attention !

Source - www.airbestpractices.com/

What can we do about it ?

Optimise work cycles Minimise cycle times

More than cylinder speed- Minimise bounce at end of

stroke- Reduce off-cushion time

delays- Minimum time between

valve switching and cylinder moving

Totalising Mass Air Flow Sensors Sensor emits an electrical

pulse after a certain volume of air is flowed

Count the pulses over time Calculate the average flow

Ultrasonic leak detectors Air leaks “Hiss”

Broad spectrum white noise Contains an ultrasonic components Leak detectors “listen” for this ultrasonic

component Loudest at the source

Ultrasonic leak detectors

Reduce leakage Best practices for tube connections

Square cuts on tube for push connect fittings Reusable fittings

- ISO “G” threads seal on a spot face with “O” ring- Don’t re-use tapered thread fittings

- Seal by deforming threads- PTFE tape

Low leakage valves- Elastomeric seals- Preferable to lapped spools

- Leakage increases over time Take advantage of air-pilot valve technology

- Lower wattage solenoid coils- 0.35 W, not 3.5W

- Especially important for spring return valves- Where coil voltage needs to be maintained

Size actuators correctly for the application Very common to guesstimate on the high side

- Just in case How fast ? How much load ? Orientation ? Web-based calculation tools are available

Optimize the actuator based on application parameters- Load - Speed - Line pressure- Tube lengths

Pressure drops in tube Easy win

Match tube diameter and length to needed flow

Example – 3/8” tube (10mm) 2400 Nl/min / 85

cfm1700 Nl/min / 60 cfm1300 Nl/min / 46 cfm

Web-based calculation tools

Size actuators correctly for the application

Reduce distances between valves and actuators Decentralised pneumatics

Fieldbus- Minimal wiring

Avoid larger valve manifolds- Multiple smaller

manifolds Lets you keep valves and

actuators closer together- Reduce tube lengths

Valve / Cylinder combinations Valve mounted on cylinder

- Best case to minimise tube lengths- Minimises dead volumes

Reduce your pressures Force = Pressure x Area

More force if more pressure – Right ?- Not the whole story

Net force = Pressure x piston area – Pressure x (piston

area – rod area) What about double rod cylinders ? What about rodless cylinders ? Need to control the DIFFERENTIAL pressure

across the piston Speed controlled by exhaust rate of second

chamber- Exhaust rate slower the higher the

pressure

Simple application, one pressure One valve

Same pressure for extend and retract

Speed limited by amount of air to be exhausted

Different pressures High pressure to extend Lower pressure for return

stroke Insert pressure regulator in

retract line Needs check valve for

exhaust line Saves energy Unexpected benefit

- Increases extend speed- Easy retrofit for

existing applications

Stroke time with 6 bar main, different “no-load” pressures

Cycle time reduction for different strokes:

2 bar “no-load stroke”

Application example Lab exercise Rodless cylinder Two ISO size 2, 3/2 valves Multiple ports 4.4 lb 36 ft / sec

Case study Press fit application

Rexroth in-house production

6 inch bore cylinder 100 psi 2800 lbf

Regulator added for return stroke 10 psi Air pressure reduced 90%

38% energy savings ROI 2100 cycles

High air consumption devices Vacuum generators

Venturi effect requires a constant air supply

Not needed after required vacuum level achieved

Air Economiser technology Vacuum switch to sense vacuum level Turns off venturi air supply while vacuum

is sufficient Turns venturi air supply back on after

vacuum level degrades Needs NO controls logic

Vacuum switch and on/off circuitry onboard

But what does it cost ? HOW MUCH air am I using ?

Need to know cylinder internal volumes- Extend- Retract- Single or double acting ?

- Do I use air on 1 or 2 strokes ?

Tube dimensions- ID- Length

Air pressure- Compression ratio

Compressor efficiency Cost per kW-hour

You could do it in Excel . . .

Or you can use online tools

Air costs with differential pressures

Conclusions If you want to be efficient and economical -

Don’t tolerate leakage- Poor installation- Aging, worn components- Fix leaks - ongoing

Size components correctly- Don’t neglect the tube size – very important- Take advantage of online tools

Use minimum pressure to do the work- Is the return stroke a “No-Load” stroke ?- Also increases speed

- Reduces cycle times Bigger isn’t always better

Thank YouFluid Power Expo

Phil O’NeillBosch Rexroth Pneumatics

Cleveland, OH10/26/2011

Energy Savings with Pneumatics

Technology