A SAFETY

VALVE

FOR

CORROSIVE

G G. Zhiburtovich, and I. Kh. Paikin

M.

F.

MEDIA

Podlipskii,

UDC

621.646.28 : 66.018.84

I n c r e a s e d r e q u i r e m e n t s a r e imposed on safety valves intended for work with c o r r o s i v e operating media, with r e s p e c t to seal h e r m e t i c i t y and a s s u r a n c e of operability when t h e r e is a c o u n t e r p r e s s u r e in the s y s t e m u n d e r conditions of accidental d i s c h a r g e of the medium for a considerable distance f r o m the zone being s e r viced. In the Central Design Office of Fittings we have developed a safety valve construction which is c h a r a c t e r i z e d by an i n c r e a s e d sea! h e r m e t i c i t y , operability at a high c o u n t e r p r e s s u r e past it; a high coefficient of flow upon accidental d i s c h a r g e of the medium; and an i n c r e a s e d guaranteed s e r v i c e life. In using this valve, thanks to the reduction in losses of operating medium and in consumption of expensive stainless s t e e l s for making t a k e - o f f pipeines, a considerable economic advantage is achieved. One of the well-known means of increasing seal h e r m e t i c i t y is the use of the working medium p r e s s u r e for sealing, which m a k e s it possible to obtain a uniform distribution of f o r c e s over the whole a r e a of the sealing surface (Fig. la). The known safety valve constructions, with supply of pressure on the cutoff organ and onto a sylphon or diaphragm drive, have a proportional character of operation and a relatively small height of rise of the cutoff organ above the seat [(1/20-1/10)d s; here d s is the diameter of the seat]; i.e,, they are low-rising. In the valve construction developed, a negative phenomenon - a significant rise in counter-pressure upon accidental discharge of the medium - is used to ensure a value of the transmission ability of the valve vchich is characteristic of fully raised safety valves. For this purpose, the diameter of the cutoff member arid, correspondingly, of the sealing surface of the seat, is increased as compared with the diameter of the orifice in

Pfo ~

111/ 1111

Pw

I-ill l i l t

_L_~

LL_Z_Z_

Pep dseal b

a

Fig. I

Fig. 2

Fig. I. Schemes of action of medium pressure on cutoff organ: a) in closed valve; b) in open valve; Pw, Pie, and Pep are the working mediur~ pressure, fully open pressure, and counter-pressure, respectively. Fig. 2. Working characteristics of valves: I) of known construction; 2) of construction developed; Pso and Pcl are the pressures at the start of opening and at valve closing, respectively; the subscripts with primes refer to proportional action valves.

T r a n s l a t e d f r o m Khimicheskoe i Neftyanoe Mashinostroenie, No. 11, pp. 13-14, November, 1976.

This material is protected by copyright registered in the name of Plenum Publishing Corporation, 227 West 17th Street, New York, iV. Y. 10011. No part ] of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, | microfilming, recording or otherwise, without written permission of the publisher. A copy of this ardcle is available from the publisher for $ Z 50. J

969

Fig. 3. Safety valve for c o r r o s i v e media. the inlet pipe (up to d s >- 1.4 Dv, w h e r e Dv is the nominal valve passage). The p a s s a g e section in the valve seal is given by F3=~dseal hfo, where dseal is the d i a m e t e r of the seaiing zone (dseai = ds); hfo is the s t r o k e in fuI1 valve opening (Fig. lb); it is i n c r e a s e d both due to the i n c r e a s e in dseal and aIso due to the i n c r e a s e in s t r o k e on complete valve opening. The e o u n t e r p r e s s u r e which a r i s e s on opening, Pop, acts under the cutoff m e m b e r with an i n c r e a s e d a r e a on the side of valve opening, and c r e a t e s a e o n s i d e r a b i e r i s e in r a i s i n g force, which e n s u r e s an i n c r e a s e in the s t r o k e of the cutoff m e m b e r . The c h a r a c t e r of valve operation is changed - a rapid two-position r e sponse in it takes place. In Fig. 2 we show the working c h a r a c t e r i s t i c s for valves of known construction and of the construction developed. As a r e s u l t of the i n c r e a s e in d i a m e t e r of the cutoff m e m b e r , the specific sealing p r e s s u r e also r i s e s , and, consequentiy, the d e g r e e of h e r m e t i e i t y of the seal is i n c r e a s e d . The Central Design Office of Fittings has developed and t e s t e d a sylph0n spring safety valve having Du = 25 ram for a p r e s s u r e Pw of 3 k g f / e m 2 (Fig. 3). The p a r t s which come in contact with the working m e d i u m a r e made of type 12Khl8N10T steel~ Teflon is used for the seal packing. Leakage in the valve seal is not m o r e than 2.5 om3/min in factory t e s t s and is not o v e r 5 em3/min a f t e r running t i m e has been accumulated. The flow coefficient of the vaIve, ~, is 0.6. The Iength of the d i s c h a r g e pipeline past the valve m a y r e a c h 50 m . The Kiev Equipment and Machinery-Building Piant is m a s t e r i n g the s e r i a l m a n u f a c t u r e of this valve.

970