Drives and Control Solutions

Motors, Control Solutions, Power Transmission and Advanced Motion Technology                                                                 

April 30, 2019

By Linda Caron, Parker Hannafin

Safe Distance in Machine Design When machine safeguarding is used one of the most relevant (and least discussed) effective measures is safe placement of the equipment in relation to the hazard. This is especially true when trying to comply with the requirements to eliminate trapped energy under ISO 13849-1 where exhaust time and volume of compressed air in the machine play a role in creating a safe condition. Considerations must include those questions posed in a risk assessment such as severity of injury, frequency of exposure and so we begin to look at all aspects of the machine design.


International Standard ISO 13855 “Safety of Machinery - Positioning of safeguards with respect to 

the approach speeds of parts of the human body.”; defines these standards. Most commonly considered is how quickly can we bring the machine to a safe state? And, how far do we place the safety equipment to the hazard? We must not forget to include the switching time for machine safety devices and exhaust rates in faulted conditions. Exhaust flow is not mentioned but ultimately is a critical part of bringing a pneumatic machine to a safe state.

The time taken to ensure the safe condition of the machine is met is a combination of products, switching time and flow rates. These calculations cannot be done until you have identified which safety products you will utilize because they all have different flow rates and exhaust times. Faulted flow rates are flow rates in the worst-case scenario and are important considerations in calculating safe distances. You really want to know your exhaust time in choosing components because ultimately these times will impact where you place your machine guards.

Now, Let’s Consider T (time interval)

DCS-Parker-4.jpgStandards do not exist to explain the correlation of exhausting and spacing leaving the engineering community to use a common- sense approach on how to integrate safety exhaust valves.

The closest the standards come is to say the “overall system stopping time”. For safety this time interval would ideally include time to exhaust however, this is not always practical. Most suppliers of pneumatic safety exhaust valves will provide their data for varying machine volumes (as follows).

Note – a machine with 150L of trapped air at 6 bar needs 7.30 seconds to exhaust in faulted condition so it may not be practical to assume full exhaust of a large machine but rather how to responsibly ensure safety and utilize this data to make the best decision for your application.

Size for Both Switching Time and Exhaust Time Where Possible

Of critical consideration before selecting equipment is its switching time and exhaust time. I would say it is good engineering practice to include the switching time and the exhaust time of such a component in the safe distance calculations when possible. Ideally, hazardous locations would be designed to utilize a small area of compressed air for rapid depressurization but this isn’t always possible for the existing situation in the case of retrofitting a machine.

Including exhaust time is not always possible given the large size of some machines which may take several seconds to exhaust. Here, sound judgement and good engineering principles come into play. Once open to exhaust, the safety valve will begin to reduce the pressure build up in the machine rapidly bringing the machine finally to a safe state. If you are unable to space by exhaust time practically, there are some additional things you can do to enhance the safety such as safe stopping devices like rod locks or clamps.

Concluding Safe Distance with Exhausting Products

Safety exhaust valves serve three primary functions. The first is rapid exhaust of compressed air. The second function is to prevent a restart if a fault is detected. The third in the case of redundant designs is to ensure both channels are operational or to fail safe / exhausted (even if no power is available).

Consider Faulted Exhaust Time

Chose the safety exhaust valve with the quickest faulted exhaust time to depressurize the machine as quickly as possible. If your machine has a volume of 5.30 ft3 (150 L) operating at 90 psig or 6 bar. The Parker P33 will exhaust in faulted condition (worst case) in 7.30 seconds. Use the manufacturer’s faulted exhaust time data to understand your situation fully.

Utilize secondary means

When the machine takes time to exhaust and an unsafe condition is still present utilize secondary means of stopping, blocking or holding a load in place such as clamping and rod locks.

Double up

If your pneumatic air supply offers enough pressure to meet the minimum operation pressure requirements of the safety exhaust valve, consider using two safety exhaust valves (as shown to the right). This is especially useful on large machines. Parker safety exhaust valves need a minimum 30 psi at P1.DCS-Parker-3.jpg

 Each safety valve requires a minimum input pressure of 30 psig

Follow the Standards which provide greater detail to the height of machine guards and the basic safe distances required for parts of the body. Further, stop-time measurement devices are to be used to measure the time it takes a machine to stop after a signal is given. Only then can the safeguarding device’s location

(ie light curtain) be established in relation to the hazard with the safety distance in consideration. Calculating where to put safety input devices like gates or light curtain is a critical step in machine design. Determine machine guard spacing prior to building and testing the machine. It’s also important to check the stop-

time device as part of your plant maintenance routine to ensure the machines stopping ability has not been compromised by wear or tampering.

Visit Parker Hannafin

Editor's Pick: Featured Article

KEBBy Mike Keefe

When selecting a motor, it is important to consider the required duty cycle to ensure the motor can meet the needs of the application.  

Knowing what type of duty cycle your motor requires will help a motor manufacturer like KEB select the best motor for your application. Watch the video below to see the most common types of motor duty cycles.



Read More



Motor Feature

EV Powertrain LinesBy Bill Sarver

What will the automotive marketplace look like in 10 years and how do I prepare for it? That’s the question foremost on the minds of the powertrain plant personnel I encounter in my work as an industry consultant.

It’s not an easy question to answer given that we are in the midst of a truly revolutionary time in the automotive industry. To address regional emissions mandates and upcoming bans on gasoline and diesel-powered automobiles, manufacturers are ramping up their focus on electric vehicles (EVs).


Product News

  • Prev
AutomationDirect has added new line reactor models and VTF (voltage time filter) series output ...
New expansion I/O modules from AutomationDirect for the BRX stackable micro brick PLC include ...
The Hydraulic Pump and Power Systems (HPS) Division of Parker Hannifin Corporation, the global ...
High performance for demanding applications. Our MOVIAXIS multi-axis servo inverter is motion ...
ABB offers a wide range of low voltage IEC motors, from classical induction motors that provide ...
The ProSafe-RS is a TÜV certified Safety Instrumented System (SIS) for use in SIL 1, 2, and 3 ...
In response to a global shift away from R410A and R22, Danfoss has added a complete portfolio of ...
Pfannenberg, Inc., a global manufacturer of thermal management technologies, has recently ...
Regal Beloit Corporation, a manufacturer of electric motors, electrical motion controls, power ...
B&R's intelligent track system SuperTrak is now available in a vertical-mount ...

Regal Beliot Grove GearRegal Beloit Corporation, a manufacturer of electric motors, electrical motion controls, power generation and power transmission components, had recently announced that its Grove Gear Stainless Steel Worm Gear Reducer has achieved third party IP69K certification.

Ingress Protection (IP) Marking rates the degree of protection provided by mechanical casings and electrical enclosures against intrusion, dust, accidental contact and water. It is published by the International Electrotechnical Commission (IEC). The IP69K rating is for high-pressure, high-temperature washdown applications. Enclosures conforming to it must not only be dust-tight, but also able to withstand high pressure and steam cleaning.

Read more







Latest News

  • Prev
ABB is proud to announce it has been selected as one of Canada’s Best Employers by Forbes Magazine ...
Keeping pace with significant advances in motor speed control technologies, the International ...

Rittal & EPLAN Pump out a Powerful Solution for Metro Vancouver

Kerrwil Publications Great Place to Work. Certified December 2019 - December 2020

538 Elizabeth Street, Midland,Ontario, Canada L4R2A3 +1 705 527 7666
©2020 All rights reserved

Use of this Site constitutes acceptance of our Privacy Policy (effective 1.1.2016)
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of Kerrwil