The term pilot ratio refers to the ratio of two, discrete areas of a piston, spool or poppet on which opposing pressures act. The pilot area, on which pilot-pressure acts, is always the larger of the two areas. Working or system pressure acts on the smaller, opposing area. This means a relatively small pilot-pressure can overcome a much larger working or system pressure. In other words, pilot ratio is like the hydraulic equivalent of mechanical advantage.
For example, consider a pilot-operated check valve with a pilot ratio of 4:1. If working or system pressure acting on the smaller poppet area, … continue reading »
A webinar presented by the International Fluid Power Society on the prevention and management of fluid injection injuries cites a study by Snarski and Birkhahn, two emergency department doctors at the New York Methodist Hospital. And it contains some sobering statistics:
Fluid injection injuries are relatively rare with around 600 incidences in North America per year. That’s the good news. The bad news is it means your average emergency department doctor may not recognize the seriousness of the situation.
High-pressure grease guns/systems account for 57% of injection injuries. Paint, hydraulic oil and similar fluids account for 18%. And diesel fuel … continue reading »
The other day while doing some fact checking for a consulting job, I had cause to review Australian Standard AS 2671-2002; Hydraulic Fluid Power-General Requirements for Systems. This Australian Standard is basically the International Standard, ISO 4413 with some amendments based on the local advisory committee’s input.
One of these amendments has to do with suction strainers. Section 8.3.3 of ISO 4413:2010, states: Unless agreed between the purchaser and supplier, filtration on pump suction lines shall not be used. Inlet screens or suction strainers are acceptable.
HOWEVER, AS 2671 replaces the above text with: Unless agreed between the purchaser … continue reading »