Elevator Information Center - Jack Replacement

Single Bottom Cylinder Replacement

Effective since October 2005 the State of Florida has issued a new rule in the Elevator Safety Code. ASME A17.1 section 3.18.3.4 Safety Bulkhead. Cylinders buried in the ground shall be provided with a safety bulkhead having an orifice of a size that would permit the car to descend at a speed not greater than 0.075m/s (15 ft/min) nor less than 0.025 m/s (5 ft/min). A space of not less than 25mm (1 in.) shall be left between the welds of the safety bulkhead and the cylinder head.

This rule pertains to hydraulic elevator cylinders installed prior to 1971. These elevators must have the cylinder replaced or have code compliant safeties added. Hydraulic cylinders are not covered under a standard elevator maintenance agreement and it is the owner’s responsibility to determine or provide documentation that their underground cylinder has a safety bulkhead.

Hydraulic elevator cylinder

The hydraulic elevator cylinder is generally beneath the elevator car, buried in the ground, and is responsible for lifting and lowering the elevator through the controlled flow of the hydraulic oil into and out of the cylinder. In the ground the cylinder can be exposed to elements in the soil that cause corrosion and electrolysis. Most of the cylinders installed prior to 1971 have only a single welded flange at the bottom of the cylinder and are unprotected from the harm of corrosion and electrolysis. These elevators may be in danger of the flange being eroded and unexpectedly rupturing, dropping the elevator uncontrollably. 

Double bottom cylinders

Since 1971 new hydraulic elevator cylinder installations have been required to have a double bottom cylinder. This type of cylinder has a safety bulkhead in addition to the bottom flange. At the bottom of the bulkhead is a relief hole. Should the flange rupture, the hydraulic oil would escape from the relief hole allowing the elevator to descend at a slow controlled rate; no more than 15 feet per minute. Also these jacks are fitted with a PVC lining to protect it from the elements of corrosion and electrolysis.

Cylinder Hole Drilled Out of Plum

Many cylinders are installed in jack holes that were driven or drilled into sand, clay or soil conditions that are not obstructed by harder rock or ledge. These types of conditions, though often easier to penetrate, can "walk" making it difficult to accomplish a plumb hole. This can prevent the new larger diameter cylinder from having sufficient clearance to be installed "plumb". This may require pulling the existing casing and drilling a new hole.

Hydraulic elevators are required to undergo an annual safety inspection and hydraulic system pressure test. During this test the hydraulic system of the elevator is tested to the maximum pressure the system can maintain. This maximum pressure is referred to as the relief pressure. The relief pressure can be up to 150% of the working pressure as per the Florida Elevator Safety Code. The working pressure is the pressure in the hydraulic system running at full speed and full weight capacity. During the annual pressure test single bottom cylinders are susceptible to rupture. The rupture is caused by the weakened cylinder flange welds due to the corrosion from the elements in the soil and electrolysis.

This annual pressure test and inspection are important to the safety of the riding public. It is better to cause a cylinder failure during this controlled test environment rather than during normal passenger use, due to the potential hazard to an unsuspecting passenger

There are other options to bring your elevator up to code. These options include adding car safeties or a plunger gripper. Car safeties are designed to clamp the elevator rails when a speed governor trips due to an over speed in the down direction. A plunger gripper is similar to the car safeties that it also will detect a car over speed in the down direction however this device would clamp onto the piston to stop the car. Although both options would satisfy the code requirement they are not recommended. Both car safeties and a plunger gripper are costly installations. Also the cylinder would remain a single bottom cylinder and be at risk of rupture after these devices were installed. In case of a rupture after the fact would mean the cylinder would have to be replaced regardless of the other safety devices.