Design calculation to prove pressure handling capability of ‘HB” Series Needle Valves (DRAWING # PBB–H-S-88-MF)

The HB Series Needle Valve assembly consists of the following major parts (Refer detailed drawing No PBB–H-S-88-MF/4 )

1. Gland Retainer2. Gland Body3. Spindle4. Lock Nut5. Retainer Washer 6. Packing Support7. Gland Washer8. Packing - Teflon

Pressure withstand capacity required of manifold

= 10,000 psi= 10,000 psi / 2.2 x 2.54 x 2.54= 704 Kg/cm2 (1 Kgs = 2.2 lbs; 1 inch = 2.54 cm)

The vee-tip of the spindle closes an orifice of diameter 4mm = 0.4cm = do

Area of orifice hole =

Force on spindle required to withstood at 10000 Psi when the valve is in closed condition

= pressure x area = 704 kg/cm2 x 0.1256 cm2 = 88.42 kg.

Pressure withstanding capability shall be checked at the following threaded joints:

1. Spindle to gland retainer threading.2. Gland Retainer to gland Body threading.3. Gland body to main body threading.

1) Pressure withstand capability calculation for spindle to gland retainer threading :

Thread type M8; Thread pitch = 1.25mm = 0.125cm = t1

Thread length = 2.0mm

do

2 = (0.4)2 = 0.1256 cm2

No of threads = threading length / pitch= 20/1.25= 16

Minimum root diameter of threading = 6.647mm = 0.6647cm = d1

Tensile / shear strength for material of Spindle is SS316 is 84 ksi

= 84000 psi = 84000 = 5918 kg/cm2 = T2.2 x 2.54 x 2.54

(1 kg = 2.2 lbs; 1 inch = 2.54 cm)

Shear withstand area of each thread

= d1 x t1 = 3.14 x 0.6647 x 0.125 = 0.26 cm2

Shear withstand area of 16 threads

= 0.26 x 16 = 4.16 cm2 = A1

Shear withstand force capability threaded spindle

= T x A1 = 5918 x 4.16 = 24618 Kgs

Factor of safety =

Shear withstand force capability = 24618 = 278.42 Shear withstand force required 88.42

Thus the spindle of gland retainer threading is adequately rated for pressure capability required.

2) Pressure withstand capability calculation for Gland retainer to gland body threading :

Thread type M16; Thread pitch = 1.5mm, = 0.15cm. = t2

Threading length = 29mmNo threads = 29/1.5 = 19.33 = 19 threads

Minimum root diameter of threading = 14.376mm = 1.4376 cm = d2

Tensile shear strength of SS316 material = T = 5918 kg/cm2

Shear withstand area of each thread = d2 t2

= 3.14 x 1.4376 x 0.15 = 0.677 cm2

Shear withstand area of 10 threads

= 19 x 0.677 = 12.863 cm2.= A2

Shear withstand force capability of above threaded joint

= T X A2 = 5918 x 12.863 = 76123 Kg

Factor of Safety = 76123 = 860 88.42

Thus, this threaded joint is also adequately rated for pressure capability required.

3) Pressure withstand capability calculation for gland body to main body threading :

Thread type M18; Thread pitch = 1.5mm = 0.15cm = t3

Threading length = 7.5mmNo of threads = 7.5mm / 1.5mm = 5 threads

Minimum root diameter of threading = 16.376mm = 1.6376 cm = d3

Tensile shear strength of SS316 Material = T = 5918 Kg/cm2

Shear withstand area of each thread = d3 t3 = 3.14 x 1.6376 x 0.15 = 0.77 cm2.

Shear withstand area of 5 threads = 5 x 0.77 = 3.85 cm2. = A3

Shear withstand force capability of above threaded joint= T x A3 = 5918 X 3.85 = 22784 Kg

Factor of safety = 22785 / 88.42 = 257.67

Thus, this threaded joint is also adequately rated for the pressure capability required.

Pressure withstanding capability shall also be checked at

4) Section A-A which is the weakest section area in the gland retainer. ( Refer Drawing No PBB–H-S-88-MF/2-1 )

5) Section B-B which is the weakest section area in the gland body ( Refer Drawing no PBB–H-S-88-MF/2- 2 )

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4. Pressure withstand capability calculation for section A-A of gland retainer ( Drawing no PBB–H-S-88-MF/2-1)

D0 = 14.376 mm = 1.4376 cmDi = 8 mm = 0.8 cm

Tensile withstand area of this section

= D02 – Di

2 ) 4

= 1.43762 – 0.82 ) 4

= – 0.64)

4

= 1.119 cm2 = A4

Tensile shear strength of SS316 Material = T = 5918 Kg/cm2

Tensile withstand force capability of this section

= T x A4 = 5918 X 1.119 = 6622 Kg

Factor of safety

= Force withstand capability available = 6622 = 74.89 Force withstand capability required 88.42

Thus, this section is adequately rated for pressure capability required.

5. Pressure withstands capability calculation for section B-B of gland body (Refer. Drawing PBB–H-S-88-MF/2-2)

Tensile withstand area of this sectionD0 = 16.376 mm = 1.6376 cmDi = 10.1 mm = 1.01 cm

= D02 – Di

2 ) 4

= 1.63762 – 1.012 ) 4

= – 1.02)

4

= 1.3 cm2 = A5

Tensile shear strength of SS316 material = T = 5918 Kg/cm2

Tensile withstand force capability of this section = T x A5 = 5918 x 1.3 = 7693.40 Kg

Factor of Safety = 7693.40 = 87.00 88.42

Thus, this section is adequately rated for the pressure capability required.

Summary: The weakest possible points of Needle Valve assembly have been found to be adequately rated to withstand a pressure 10,000 psi.

The Bar Stock Stainless steel body sections (Drawing # PBB–H-S-88-MF/1) are even more rated to withstand the pressure capable and hence not checked.