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 ProTalk - Hydraulics


Q. How can I stop my JIC-37 degree hydraulic fittings from leaking without over-tightening them?

Q. Are forged hydraulic adapters better than brazed styles?

Q. How does the working pressure of a hydraulic hose differ from its burst pressure?

Q. What are the advantages of using fluid power over mechanical power transmission?

Q. What are the benefits to adding case drain flow meters to my customer's hydraulic pumps and motors equipped with case drain lines?

Q. How can I stop my JIC-37 degree hydraulic fittings from leaking without over-tightening them?
A. Although the JIC fitting has become the world's most commonly used hydraulic connection, it can leak because of its metal to metal sealing surface, which is subject to damage before installation and when being re-used. A new sealing device, the flaretite seal, eliminates the problem of weeping or leaking. It is a stainless steel stamping with a convoluted surface and coated with sealant. When inserted into a flared hydraulic fitting, the ribbed design and coating fill imperfections in the seal surfaces. Flaretite seals are offered through Eaton Aeroquip and are available in 1/4" through 2" sizes.

Q. Are forged hydraulic adapters better than brazed styles?
A. Yes. Because a forged adapter is formed from a single piece of metal, it is inherently stronger than brazed, which is made up of two or more components. A brazed adapter has the possibility of leakage or failure at the joints. When given the option, choose forged.

Q. How does the working pressure of a hydraulic hose differ from its burst pressure?
A. The working pressure of hydraulic hose is the maximum pressure a hose should be subjected to. The burst pressure of a hose is that point at which a new piece of hose will fail during a pressure test. While the burst pressure is typically a 4 to 1 ratio of the working pressure (example: 10,000 psi vs. 2500 psi), it should not be considered a safety factor. Always select a hose that is rated at or above the maximum pressure of the hydraulic system in which it is being used. Often, this may be higher than the relief settings.

Q. What are the advantages of using fluid power over mechanical power transmission?

A. Advantages of Fluid Power
1) Actuators can be stalled under full load at full pressure without any damage (thanks to the relief valve limiting max pressure). (Consider what happens to an electric motor if it's stalled.)
2) Actuators can be reversed instantaneously under full load at full pressure without any damage. What would happen if you slammed your car (with a manual transmission) into reverse at 55 MPH?
3) Actuator speed and force or torque (force from cylinders and torque from hydraulic motors) on both hydraulic and pneumatic systems are infinitely variable. Changing speed and torque on many mechanical PT systems requires sprocket size changes, or sheave size changes that may or may not require longer or shorter chains and belts. Changing speed and torque on mechanical gear boxes requires new gear sets at best, and new gear boxes at worst.
4) Higher power density is easily achieved with fluid power. You can hold a hydraulic motor capable of transmitting 20 HP in one hand. Try picking up a 20 HP electric motor with one hand!
5) Fluid power systems are quieter than their mechanical PT counterparts (if the fluid power system is properly designed for low noise levels from the start).
6) Fluid power systems are intrinsically safe. You can run hydraulic cylinders and motors in an explosive environment without any special enclosures. However, solenoid valves and all electric motors and controls MUST be explosion proof, or located outside of the explosive environment.
7) More flexible machine design is a snap. With hydraulic hoses or pneumatic tubing, actuators can be mounted anywhere on the machine in any orientation. With mechanical PT, chains and sprockets as well as belts and sheaves must be in straight alignment to avoid short chain, sprocket, belt or sheave life.
8) Because all hydraulic and some pneumatic components are internally lubricated by the hydraulic fluid or a lubricator in an air line, fluid power components can last for decades without the need for external manual or automatic lubrication (if the system is designed properly from the start, and the fluid and filters are monitored and changed as required). Even when ignored and abused, fluid power components can outlast their mechanical PT counterparts (depending on the degree and duration of the abuse and neglect). Running a hydraulic pump with a restricted inlet can result in pump failure in a matter of hours. Highly contaminated hydraulic fluid or dirty, wet compressed air can lead to rapid pump, valve and actuator wear and failure.
9) Fluid power systems (with adequate training) can be safer than mechanical PT systems with their whirring chains, sprockets, belts and sheaves.

Disadvantages of Fluid Power
1) Fluid power systems are typically less efficient than their mechanical PT counterparts. Hydraulic systems are typically 85-90% efficient, while mechanical PT systems can be as high as 98-99% efficient.
2) Fluid power systems can be extremely dangerous without adequate training and/or maintenance.
3) Fluid power systems can leak hydraulic fluid or lubricated compressed air if not designed and maintained correctly. Besides being a housekeeping headache, spilled or leaked hydraulic fluid poses a serious slip/fall hazard. If an employee or visitor falls, the lost time, accident consequences and potential liability losses from the inevitable lawsuits that follow can add up to millions of dollars. Also, hydraulic fluid or compressed air line lube oil lost to external leakage represents a significant cost to dispose of and/or replace.
4) Fluid power systems can be very noisy if improperly designed and/or maintained.
5) Hydraulic fluid and compressed air MUST be monitored and maintained for cleanliness and wear (yes, hydraulic fluid and compressed air lube oil can wear out prematurely if exposed to excessive heat, dirt and/or water contamination). Even with proper monitoring and maintenance, hydraulic fluid and compressed air line lube oils have a finite life; the additives (anti-wear, anti-foaming, viscosity stabilizers etc.) eventually wear out and can actually come out of solution and become contaminants!
6) Hydraulic fluids and lubricated compressed air can present a serious fire hazard around hot processes such as steel making, aluminum extruding, etc. A pinhole leak in a high pressure hydraulic line can become a blow torch in the presence of red hot metal or an open flame. Many plants have been severely damaged or burned to the ground from an unfortunate hydraulic or compressed air line blowing off or leaking significantly at the wrong time or place. Fire resistant hydraulic fluids (water glycols, phosphate esters and polyol esters, for example) have gone a long way to mitigate fire hazards from fluid leaks in proximity to hot manufacturing processes. But with high pressure atomization and a hot enough heat source, most any hydraulic fluid can be made to burn.

As you can see, fluid power systems offer more advantages than disadvantages. And with proper system design and maintenance, leaks and noise can be a thing of the past.

Q. What are the benefits to adding case drain flow meters to my customer's hydraulic pumps and motors equipped with case drain lines?
A. Case drain flow meters accurately monitor case drain flow so you know when to replace or rebuild the pump or motor before a catastrophic failure occurs. They help confirm pump performance, identify required maintenance, and prevent/minimize unscheduled downtime. The sealed window tube makes the unit suited for outdoor/exposed applications and where wash-downs may be required.




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