Hydraulic machinery exceeds nearly every other mechanical form of power transmission when it comes to working in extreme environments. Excavators, tree harvesters, mining and tow trucks and other hydraulic vehicles perform the harshest tasks on uneven terrains with heavy loads that apply tremendous forces on hydraulic systems.
These tasks can generate extreme shock and vibrations, as well as dramatic changes in temperature, dust and moisture. In addition, pressure spikes/impulses generated within hydraulic systems can present a significant challenge to the reliability of internal components like pressure instruments.
So, how can you optimize the performance of your mobile hydraulics against hazards?
Pressure control and monitoring devices are key to controlling hydraulic systems and improving power, flexibility, speed and safety. They control and monitor hydraulic fluid pressure levels to supply the necessary force to overcome resistance. They also monitor unsafe conditions, trigger alarms or automatically shut down hydraulic pumps to prevent overpressure conditions.
During my time working in this industry, I’ve learned how to correctly apply pressure transducers in mobile hydraulics control systems.
This article will help you with the challenges of pressure control and measurement including shock, vibration, pressure spikes, pulsation and environment, and show you how to keep your mobile hydraulic machines in optimal shape.
Shock, Vibration and Spikes in Hydraulic Applications
Let’s start by looking at the hazards that can impact the performance of the pressure transducers in your mobile hydraulics. Shock, vibration, pressure spikes and pulsation can all create a challenge for your equipment.
Shock and vibration can be caused by any disturbance that creates noise, sudden impact that involves overcoming friction loads, or uneven terrain that changes fluid flow within the system.
For instance, an excavator generates high shock when it accidentally hits a solid rock, lifts an excessive load or drops it.
Likewise, a mining dump truck’s hydraulic shocks can experience extreme shock by the weight shifts from loading or by going over potholes. And the mining truck brake system produces high shock conditions when the truck brakes abruptly.
Shock
Hydraulic shock is the sudden change in fluid velocity in the system, which may have been caused by an external impact. Your pressure instrument must withstand the physical impact, the sudden change in fluid velocity and the sudden stop.
Many are impacted by short frequency/high amplitude pulses. Unlike air, hydraulic fluid is non-compressible and pressure spikes in the system can increase four to five times over the normal operating pressure. That affects the performance and lifespan of pressure instruments if they are not strategically designed and protected.
Vibration
Vibration is a mechanical oscillation or noise that occurs occasionally or indiscriminately because of noise from motors, pumps, actuators, valves, hydraulic lines and other components.
It can generate flow ripples, which connect with hydraulic components such as transmission lines and valves to create harmonic pressure waves. Hydraulic vibration is mostly high frequency/low amplitude pulses that also affect the performance and lifespan of pressure instruments if not strategically designed and protected.
Pressure Impulse/Spikes
Pressure Impulses (or pressure spikes) can also occur in hydraulic systems when fluid flow rates change quickly. Like water hammer, actions such as a valve closing can cause a significant short-duration, high-magnitude pressure wave within the hydraulic system.
These pressure spikes in hydraulic systems can easily reach many times the normal operating pressure in microseconds. Pressure instruments are generally “dead-ended” devices and can be impacted or damaged by pressure spikes if not properly located and protected.
Pressure Transducers in Mobile Hydraulics
Pressure transducers can be damaged under shock and vibration operating conditions if not appropriately designed. Pressure transducers for mobile hydraulic applications must have compact sensing elements, shorter wire bonds, a coplanar design, and a small footprint to withstand shock and vibration.
To meet the above requirements, Ashcroft developed our CVD thin film pressure sensor with high stability, accuracy and wide operating temperature ranges. In addition, we use a silicone gel that absorbs shock and vibration to protect delicate wire bonds, which connect the sensor element to the electronics. Figure 1 shows the cross-section of the Ashcroft GV pressure transducer enhanced design for vibration and shock application.
Figure 1- Ashcroft GV Pressure Transducer with enhanced Vibration and Shock Protection
The Ashcroft® S1 OEM pressure transducer incorporates the CVD sensing technology to provide a cost-effective transducer that provides superior performance. The S1 is a hydraulic pressure sensor designed for applications that see high shock, vibration and excessive pressure cycling. It's an ideal choice for pressure measurement for mid- to high-volume applications.
Pressure transducers can be damaged under the continuous operation of pressure spikes and pulsation. The common effect of pressure spikes and pulsation is positive zero shift, and there are several choices to protect transducers such as throttle screws, snubbers and capillary lines depending on the application.
Protecting the Pressure Transducers
Here are some tips I’ve found to be successful in protecting pressure transducers used in mobile hydraulics:
- Removing air from the hydraulic system significantly reduces the magnitude of hydraulic pressure spikes.
- Avoid placing pressure transducers at the end of long and/or straight runs of pipe.
- Consider using the highest-pressure range transducer to meet application requirements.
- Install pressure snubbers or dampers between the process and the pressure instrument connection with different grades of porosity selection for protection.
- Install a throttle screw or plug in the process connection to dampen pressure spikes and pulsation.
- Install capillary lines to remote mount the pressure instrument away from shock and vibration. This prevents pressure spikes and pulsation by restricting the throttling effect due to the small size tubing.
- Dampeners are a cost-efficient and effective choice to prevent the damaging effects of pressure spikes and pulsation.
Pressure Switches in Mobile Hydraulics
A high-quality pressure switch for use in mobile hydraulics should not be sensitive to shock or vibration but should react to pressure pulses between 5 to 10 milliseconds. Premature switching can occur if pressure spikes or pulsation overcome the set point.
Throttling devices are also used to minimize pressure spikes and pulsation. Remote mount pressure switches in a shock and vibration-free location with capillary is the best practice to eliminate pressure spikes or pulsation, or a pressure snubber can be installed between the process and pressure switch to dampen pressure spikes and pulsation.
Protecting Pressure Gauges
Digital pressure gauges are less vulnerable to shock and vibration than analog or mechanical pressure gauges, but it is a good practice to protect all pressure devices for better performance. The impact of shock and vibration will damage mechanical pressure gauges in several ways:
- Pressure spikes and pulsation effects are clearly visual on mechanical pressure gauges as the pointer upsurges rapidly in response.
- If the pointer fluctuates, it’s difficult to accurately read the pressure gauge.
- Pressure gauge movement will wear the gear teeth across the segment when exposed to low frequency/high amplitude signals known as pressure spikes.
The best practice to prevent damage from shock and vibration is to remote mount pressure gauges with capillary. For analog gauges use a fill liquid such as glycerin or silicon. Ashcroft offers liquid fill substitutions such as PLUS!™ Performance.
Throttle screws or throttle plugs installed in the pressure gauge process connection can restrict the flow and minimize pressure spikes and pulsation. You can also use pressure snubbers or dampers installed between the process and the pressure gauge.
Pressure Instrument Classifications
Mobile hydraulics applications require pressure instruments that offer the most rugged electrical, mechanical and environmental protection, due to the extreme outdoor dynamic and remote operating conditions.
There are two types of enclosure protection classifications: National Electronic Manufacturers Association (NEMA) ratings and Ingress Protection (IP) ratings. Though NEMA and IP ratings are not identical, they are similar and can often be used interchangeably for rating enclosures of pressure instruments.
IP ratings specify standards for protection against the ingress of solid foreign objects or liquids, while NEMA ratings also specify protection against other conditions, such as corrosive agents.
Typically, most pressure instrument manufacturers define the instrument temperature specifications on the datasheet. Pressure transducers with NEMA 4 or IP66 ratings and above are acceptable to be used in most mobile hydraulics.
NEMA 4 Enclosures are acceptable for outdoor use, provide a degree of protection against falling dirt, rain, sleet, snow, windblown dust, splashing water or hose-directed water, and will be intact by the external formation of ice on the enclosure. IP66 offers protection against dust and low-pressure jets of water from all directions.
We don't like to pressure you, but we have more information.
Mobile hydraulic systems require strength capacity, fast response, and precise control that is possible with the assistance of pressure instruments such as pressure transducers, pressure switches and pressure gauges.
I hope you have a better understanding of the importance of quality pressure instruments in your mobile hydraulics. The Ashcroft A series is a great place to start your research.
For more information about pressure transducers, check out some related articles:
- Choosing the Right Pressure Sensor
- Selecting Electrical Connectors for Pressure Transducers
- Product Review: S1 OEM Pressure Transducer
- How Does Media Temperature Affect Pressure Transducer Performance?
Contact us today to talk to one of our industry experts and get all your questions answered. Or learn what mistakes to avoid when selecting pressure sensors in our eBook: