ASME PTC 25:1998 pdf free download

ASME PTC 25:1998 pdf free download.Pressure Relief Devices.
built-up back pressure — pressure existing at the outlet of a pressure relief device caused by the flow through that particular device into a discharge system
burst pressure — the value of inlet static pressure at which a rupture disk device functions
chatter — abnormal rapid reciprocating motion of the movable parts of a pressure relief valve in which the disk contacts the seat
closing pressure — the value of decreasing inlet static pressure at which the valve disk reestablishes contact with the seat or at which lift becomes zero coefficient of discharge — the ratio of the measured relieving capacity to the theoretical relieving Capacity
cold differential test pressure — the inlet static pressure at which a pressure relief valve is adjusted to open on the test stand. This test pressure includes corrections for service conditions of superimposed back pressure and/or temperature
constant back pressure — a superimposed back pressure which is constant with time
cracking pressure — see opening pressure flow capacity — see measured relieving capacity
flow-rating pressure — the inlet static pressure at which the relieving capacity of a pressure relief device Is measured
flow resistance — a dimensionless term (such as used in para. 5.5.7) which expresses the number of velocity heads lost due to flow through a rupture disk device (where velocity head is one-half the velocity squared divided by the acceleration of gravity)
flutter — abnormal, rapid reciprocating motion of the movable parts of a pressure relief valve in which the disk does not contact the seat
leak pressure — see start-to-leak pressure leak test pressure — the specified inlet static pressure at which a quantitative seat leakage test is performed in accordance with a standard procedure marked breaking pressure — the value of pressure marked on a breaking pin or a shear pin device or its nameplate
marked burst pressure — the value of pressure marked on the rupture disk device or its nameplate or on the tag of the rupture disk and indicates the burst pressure at the coincident disk temperature marked set pressure — the value or values of pressure marked on a pressure relief device
(f) Decrease inlet pressure slowly and again record reseating pressure of valve and back pressure.
(g) In most instances, it is desirable, or a requirement, that the valve be tested over a given range of back pressure. In such cases, it is convenient if the value of back pressure chosen in (a) above be either the lowest or highest of this range. Back pressure may then be increased or decreased in increments, repeating (a) through (h) above at each incremental value.
4.8.5 Testing With Built-lip Back Pressure (Fig. 6)
(a) Increase the pressure at the valve inlet. During the pressure interval starting at 90°lo of the expected set pressure, the rate of pressure increase shall not exceed 2.0 psi/sec, or whatever lesser rate of increase is necessary for the accurate reading of the pressure. Observe and record the set pressure of the valve and any other desired or pertinent characterist cs.
(b) Continue increasing the pressure at the valve inlet until the valve remains open. Adjust built-up back pressure to desired value. Observe the action of the valve. Gradually decrease the inlet pressure until the valve closes. Record the reseating pressure of the valve and back pressure. Observe the action of the valve.
Cc) Repeat paras. (a) and (b), recording set and reseating pressures, and back pressure, until all are established and stabilized.
(d) Establish and maintain flow-rating pressure until flow instruments and back-pressure gage indicate a steady-state condition.
(e) Record the following:
(1) valve-inlet pressure;
(2) valve-disk lift;
(3) liquid-inlet temperature;
(4) flow-meter differential pressure;
(5) back pressure.
(g) Decrease inlet pressure slowly and again record reseating pressure of valve and back pressure.
(h) In most instances, it is desirable, or a requirement, that the valve be tested over a given range of back pressure. In such cases, it is convenient if the value of back pressure chosen in para. 4.8.4(a) be either the lowest or highest of this range. Back pressure may then be increased or decreased in increments, repeating (a) through (h) above at each incremental value.