POP PINS, POP PIN ASSEMBLIES AND SPRING PLUNGERS
In the fitness industry pop pins, which
go by several names including, pop pin assemblies, retractable
spring plungers and retractable spring loaded plungers are
widely used on residential and commercial strength equipment
for various purposes. Some common functions are to set and
lock in seat height, range of motion (ROM) settings, back pad
adjustments and roller pad comfort settings.
The pop pin assemblies consist
of a plunger, a compression spring, a threaded locking cap
and a knob. Although pop pin assemblies appear to be a minor
part of a piece of single station strength unit or a home gym,
they really fill important roles. If they are not functioning
at all, a seat may have to be used at the lowest setting, making
a position like a pec deck unusable for all but the tallest
users or if the pop pin is used to set a range of motion on
a position like a leg extension, it could force the user to
have an incomplete exercise or to have to over extend just
to start the exercise.
More serious failures are
when they slip out of the setting during use, while under a
load. This type of failure could easily cause a serious injury
to the user.
Several thing can go wrong
with these retractable spring loaded plungers. A common problem
is that the pull knobs, which could be round knobs, T-knobs
or draw knob style, can come off and get lost. Although this
problem is easily resolved by replacing the missing knob, in
the meantime, the ROM adjustment or seat adjustment can't be
used. Another common failure is that the internal compression
springs break or lose their strength. This is a serious failure
because the tip of the plunger may not stay engaged throughout
the complete exercise routine. Once again, this type of failure
can cause serious injury to the user. Occasionally, the plunger
it self breaks, but more often, the functional tip of the plunger
will wear and when that happens, the pop pin won't stay in
place when under a load.
Frequently, what is reported
as a failure of a pop pin is actually wear of the receptacle
holes on the range of motion cam or the seat support or some
similar device, that the tip of the pop pin plunger locks into.
With wear, the holes in the range of motion cam or seat support
tube, get elongated or oversized, which causes the pop pin
assembly to slip out of place at times, depending upon which
settings were chosen.
Routine preventive maintenance
of strength equipment should include an examination and lubrication
of the pop pin assemblies to ensure that the are safe and that
they continue to function as designed.