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Subchapter 6. Elevator Safety Orders
Article 18. Design Data, Formulas, Tests on Approved Devices, and Electrical Regulations

§3102. Hydraulic Plunger, Cylinder, and Piping Design.

(a) Plunger Design. Plunger shall be designed and constructed in accordance with one of the following formulas.

(1) Where slenderness ratio of plunger is less than 120:

W/A = 13600 - 0.485(L/R)2

(2) Where slenderness ratio of plunger is greater than 120:

W/A = 95,000,000/(L/R)²

Where:

W = Allowable gross weight to be sustained by plunger. Where a counterweight is provided, the weight of the counterweight plus the unbalanced weight of the counterweight ropes may be deducted in determining W. In determining W, 1/2 of the weight of the plunger shall be included. Where the cylinder is attached to the car frame, the weight of the cylinder, the liquid in the cylinder, and 1/2 the weight of the plunger shall be included.

A = Net sectional area of plunger (area of metal) in square inches.

L = Maximum free length of plunger in inches.

R = Radius of gyration of plunger section in inches.

W/A = Maximum allowable fiber stress.

EXCEPTION: Plungers having a free length of 25 feet or less may be accepted without further examination for strength and elastic stability provided all of the following conditions exist:

1. The working pressure is 300 pounds per square inch or less.

2. The plunger is 4 inches nominal pipe size or larger.

3. Pipe not lighter than schedule 40 is used and not more than 1/16 inch of metal has been removed from the wall thickness in machining.

4. The plunger is not of the telescoping type.

FIGURE 3102 A1

FIGURE 3102 A2
ALLOWABLE GROSS LOADS

(3) Figures 3102 A1 and 3102 A2 may be used as a guide for the maximum free lengths for various loads on some of the more common pipe sizes used for plungers.

(b) Design of Joints in Plungers. Plungers composed of more than one section shall have the joints designed and constructed to:

(1) Carry in tension the weight of all plunger sections below the joint, and

(2) Transmit in compression the gross load on the plunger with a factor of safety of not less than 5 based on ultimate strength.

(c) Attachment of Plunger to Platform. The plunger shall be attached to the car platform with fastenings of sufficient strength to support the weight of the plunger with a factor of safety of not less than 4.

(d) Plungers Subjected to External Pressure. For plungers subjected to external pressure, the working pressure shall be not more than that indicated by the following formula:

(1) Where the ratio of t/d is less than 0.023:
3102

(2) Where the ratio of t/d is greater than 0.023:

P = 28890 t/d - 462

Where:

p = Working pressure in pounds per square inch.

t = Finished wall thickness in inches.

d = External finished diameter in inches.

(e) Cylinder Design

(1) Cylinders shall be designed and constructed in accordance with the following formula:


               pd
          t =  --
               2S

Where:

t = Thickness of wall in inches, minimum.

p = Working pressure in pounds per square inch.

d = Internal diameter in inches.

S = Design stress in pounds per square inch (12,000 psi maximum for mild steel and 1/5 the ultimate strength for other metals).

(2) Gray cast iron (or other brittle material), if used in the cylinder assembly, shall have a factor of safety of not less than 10.

(f) Cylinder and Plunger Heads.

(1) Heads of cylinders, and heads of plungers subject to fluid pressure, shall conform to the following requirements:

(A) They shall be designed and constructed in accordance with the applicable formulas in 3102(f)(2), provided that steel heads shall in no case have a thickness less than that required for the adjoining shell.

(B) Dished seamless heads, convex to pressure, shall have a maximum allowable working pressure not more than 60 percent of that for heads of the same dimensions with pressure on the concave.

(C) Reinforced heads shall be designed and constructed so that the maximum stress at rated capacity shall not exceed 12,000 pounds per square inch for mild steel and 1/5 of the ultimate strength of the material for other metals.

(D) Pressure heads subjected to mechanical loads in addition to fluid pressure loads shall be so designed and constructed that the combined stresses will not exceed the limits specified in Sections 3102(f)(1)(A), 3102(f)(1)(B), and 3102(f)(1)(C).

(2) Heads of cylinders and heads of plungers subject to fluid pressure shall be designed and constructed in accordance with one of the following applicable formulas:

(A) Flat unreinforced heads:

t = d multiplied by the square root of (p / 4S)

(B) Dished seamless heads, concave to pressure:

t = 5pr / 6S

Where:

t = Thickness of head in inches, minimum.

d = Diameter of head between supporting edges in inches.

p = Working pressure in pounds per square inch.

S = Design stress in pounds per square inch (12,000 psi maximum for mild steel and 1/5 of ultimate strength for other metals).

r = Radius to which head is dished, measured on concave in inches (not greater than d).

(3) Welding of parts on which safe operation depends shall conform to Section 3033(g).

(g) Pipe Design.

(1) The minimum wall thickness of pipe for working pressures over 250 pounds per square inch shall be determined by the following formula:

t = (pD / 2S) + C

Where:

D = Outside diameter of pipe in inches.

t = Minimum wall thickness in inches.

p = Working pressure in pounds per square inch.

O.050 for threaded pipe up to 3/8 inch pipe size
Depth of thread in inches, for threaded piped over 3/8 inch pipe size.
Depth of groove inches, for grooved pipe.
0.000 for other pipe of unreduced thickness.

S = Allowable stress in pounds per square inch (1/5 ultimate strength).

(2) Supply piping materials and fittings shall conform with the applicable provisions of USAS B31.1.0 except that non-ductile material shall not be used. The material used shall have a factor of safety of not less than 5 based on ultimate strength and on elongation of not less than 10 percent.

(3) Plain end nonferrous pipe or tubing shall have a wall thickness not less than that determined by the formula in Section 3102(g)(1) where C = 0.000 and S (max) 1/5 of the ultimate strength of the material used.

(4) Welding of parts on which safe operation depends shall conform to Section 3033(g).

(5) Threads if piping, fittings, and valves shall conform to USAS B2.1.

HISTORY

1. Amendment of subsection (a)(2) filed 11-24-76; effective thirtieth day thereafter (Register 76, No. 48).

2. Editorial correction of subsection (f)(1)(D) (Register 95, No. 34).

3. Editorial correction of subsections (e)(1) and (g)(1) (Register 95, No. 41).

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