18 years ago
I'm trying to design a foot pump jack for use on hospital gurneys to
raise and lower the bed. It's set up just like a bottle jack and is
pumped up and then pressing a relief valve lets the bed back down.
The problem is, in looking at one, it doesn't appear to work like I
thought. The pump is connected to the bottom of the cylinder and
pumps oil under the piston. The intake of the pump is connected to a
relief valve which is, in turn connected above the piston on the
cylinder, sucking oil from the upper chamber. Simple, right?
Well, for some reason the upper port of the cylinder is connected to
the *middle* of the cylinder (there is no port in the top cylinder
head). So the piston actually passes over it on the way to the top,
leaving the oil chamber open to both ports!
Are any of you familiar with this design?