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In our last two posts, we discussed Type A and B safeties,
referred to respectively as "A - instantaneous applied safeties" that apply
quickly and cause the elevator to stop suddenly, and "B – flexible guide or
wedge type safeties" that apply at a slower rate for higher speed elevators. In
this article, we move onto Type C Safeties and counterweight safeties. As
mentioned before: Please keep in mind that there are many variations of safeties
and we are not going to cover them all. I can provide information upon request
for specific applications.
Type C safeties are basically of the design that uses the
Type A instantaneous safeties with higher speed elevators and to prevent the
shock of the sudden application of the safeties an oil-filled buffer, which can
thought of and compared to a heavy-duty shock absorber. This buffer assembly is
interposed below the platform connected to the car safety-plank and then to a
traveling auxiliary safety-plank that has the safeties mounted on it. Think of
a separated but attached assembly below the elevator that collapses when the
safeties are applied.
When the
safeties are activated, the auxiliary safety-plank stops "instantaneously" and
the elevator continues down as far as the buffer allows at a retardation rate
to the auxiliary safety-plank. The length of the buffer stroke determines the
stopping distance. Buffer stroke is determined by the speed and mass of the
elevator. I've attached three photographs: #1 shows the buffer and framework,
#2 the right-hand side safeties, and #3 the left-hand side. I didn't have a full
photo that shows the assembly in one piece, and my artistic skills may have worn
out their welcome, but I made another feeble attempt.
Image 1
Image 2
Image 3
Type C safeties are activated via an over-speed governor
and attached rope to the safeties assembly, like A & B safeties. These
safeties are also similar to A & B safeties in that they are positioned on
each side of the two guide rails and travel with the elevator. With the retardation of the setting force by
the buffer, this makes for a smoother stop.
In the next post we will briefly look at counterweight
mounted safeties and applications that require that feature.
- Joe
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