Safeties on hydraulicsgreenspun.com : LUSENET : Elevator Problem Discussion : One Thread
Hi guys, I noticed someone posted a question about this before, but what I need to know wasn't answered. Our building (it's only 2 floors, but still) has a hydraulic elevator and I was wondering... are there hydraulic elevators out there that don't have safety devices or are they all to come with some sort of standard safety catch device? I live in Canada by the way.
-- Jim Kay (email@example.com), August 26, 2004
Repeat of Answer - There are no requirements for ALL hydraulic elevator to have a Safety with the exception of single-bottom Direct-Acting Hydraulic elevators (those manufacturered before 1972). Cathodic protections have been traditionally relied on to prevent electrolysis a very bad effect, one which commonly requires replacement of 5 to 10% of the present inventory every year. This effect has caused fatalities and severe injuries almost every year. Present Code has addressed single- bottom direct-acting jacks with the adoption of retrofit requirements of replacement of the jacks or addition of plunger grippers; but the lack of an equivalent traction (electric) elevator type Safety requirement still potentially allows for uncontrolled movement due to other failures of the pressure system. For instance, though equiped with rupture valves, the differential pressures to cause them to close will allow slight overspeed, full speed and slower uncontrolled movements, those typically experienced with a failure of the jack due to electrolysis along the sides of the jack and victaulic fitting failures. THough a completer line break will caused these valves to stop the fall, there still are many unprotected failure modes. All elevators are required to have buffers (or bumpers) and the buffers of all elevators are only designed for a slight overspeed at full load impacts. Free falls will only temporarily slow down the elevator during the bending, deflection and destruction of the buffer. It is not designed for this impact.
Measurements of one hydraulic whose fall from 6 feet generated a speed of over 1,200 fpm (6 m/s) before it impacted. This was with only a 2 sq. in. ball valve opened to atmosphere in a study I carried out. I hope this answers your questions.
-- John Koshak (firstname.lastname@example.org), September 01, 2004.
In my experience, more jacks don't have cathodic protection than do. Unless one includes PVC, protective wrapping, etc. in that category, which I believe is technically incorrect.
Many jacks, especially older ones, have NO protection whatever.
Rupture valves will only defense against a feed line rupture. A properly designed rupture valve responds to the drop in pressure accompanying an increase in velocity and should close promptly before any dangerous velocity is reached.They do not protect against a sudden massive rupture of the cylinder proper, as the cylinder is "downstream".
The good news is that such failures are very rare indeed.Usually, a failing cylinder will develop a slow leak, gradually increasing. This should be a warning that stimulates corrective action well before a "blow out".
At the risk of being a bit picky, the maximum speed attained due to the acceleration of gravity by a body falling from rest a distance of six feet, neglecting air resistance, the resistance, if any, of the opening to oil flow, etc. is about 1179 fpm.
-- John Brannon (email@example.com), September 03, 2004.
Most hydraulic elevators do not have a "standard safety catch device". In Canada, it is only a requirement for the elevator to have safeties if it is classified as a roped hydraulic. Contrary to another answer that you have received, there is no retrofit requirement for single bottom cylinders in Canada.
We would recommend that any owner of an elevator that has a single bottom, unprotected cylinder, strongly consider having it replaced with a PVC encapsulated unit.
-- Robert Twilt (firstname.lastname@example.org), September 18, 2004.