Inlet pressure drop

In the case of set pressures below 100 KPa gage (since pressure drop becomes proportionately larger) the maximum inlet pressure drop at design flow rate may be extended to 5% of set pressure (KPa, gage). The purpose of this requirement, which applies to both conventional and bellows type valves, is to prevent chattering. 

Chattering caused by undersized inlet piping may sometimes be eliminated on pilot operated PR valves if the pilot valve pressure tapping is taken directly from the vessel being protected. However, it is recommended that the above inlet pressure drop limitations still be applied, to avoid the capacity reduction that would result from excessive inlet losses and to ensure freedom from chatter. 

Inlet piping is held to a minimum, with the safety device preferably mounted directly on the equipment and with the total system pressure drop loss to pres.sure relief valve inlet not exceeding 3% of the set pressure in psig, of maximum relief flowing conditions [10]. To conform to code (see ASME code. Sect. Vlll, Div. l-UG-127 [1]) avoid high inlet pressure drop and possible valve chatter ... 

M7 - The inlet pressure drop between the protected pressure point and the relief valve (between P, and P2) must be 3% or less (Figure 4.10). 

A sharp-edged penetration, as shown in the middle figure, results in a configuration that creates a pressure drop equivalent to 18 straight pipe diameters. Add to this the actual length of the inlet riser for total inlet pressure drop calculations. 

Earlier in this book, we cautioned against using the type of changeover valves or inlet isolation valves related to inlet pressure drops. The main factor here is the Cv (valve flow coefficient) value of the changeover device or block valve used upstream of the SRV. If individual foil-bore valves are used, the same principle applies as for changeover valves. Note once more, however, that if individual valves are used upstream of an SRV, they must be interlocked if used in a switch-over system or locked open if used in an individual isolation... 

The non-mandatory portion of ASME VIII Division I also includes the 3% limitation. Inlet pressure drops higher than 3% of the set pressure may result in valve instability and chatter as discussed in Chapter 6. Due to the lack of conclusive experimental evidence, industry has generally accepted the 3% rule as the standard. 

Inlet pressure drops were evaluated based on the frictional losses only between the adjacent equipment and the relief device. Per API RP 520 Part II Section 2.2.2, inlet pressure drops were calculated based on the actual rated capacity of the relief valve. 

The phenomenon of blowdown is caused by the use of springs. The valve spring balances against a pressure that equals the pressure in the protected tank minus the kinetic effects. When the PSV is open, its inlet pressure is less than the pressure in the protected vessel because of the inlet pressure drop. Blowdown is the amount by which the protected tank s pressure has to drop below the PSV s set pressure for the valve to reseat. The normal blowdown of a PRV is between 2 and 7% of set pressure. Pilot-operated PRVs can reduce the blowdown to about 2%. 

In the apparatus to be used in this experiment (see Fig. 3), the gas contained in bulb B flows through the capillary tube over a time period tf during which the inlet pressure drops from a predetermined initial value P to a predetermined final pressure Pi The outlet pressure p2 is constant at the ambient atmospheric pressure during this period. The volume V occupied by gas below the capillary (bulb B plus the pressure gauge and associated tubing) is constant, but the number of moles n of gas contained in volume Kvaries according to the ideal gas law ... 

Using the notation of the pipe run shown in Figure 4.2, we have the following equations relating mass flow and inlet pressure drop ... 

Compressor outlet temperature T2ea in °K and °C, due to compression efficiency r]c and the inlet pressure drop A Pi. 

In July 2012 another penalty fine (the third and final) was settled. At that time BP agreed to pay more than 13 million and abate violations in settlement agreement with OSHA. Penalty stems from citations for more than 400 PSM violations cited at the Texas refinery in October 2009. OSHA cited BP for willful violations of the PSM standard, including failing to follow industry-accepted engineering practices for pressure relief safety systems, including relief valve inlet pressure drops [24]. 

The inlet pressure drop may be more or less important than that inside the capillary [743]. 

Since the inlet pressure drop, is strongly dependent on the behavior of the melt a change in the inlet geometry would be expected to influence the pressure drop as well as the elastic and shearing strains. 

The experimental data obtained by Han [735] with PE at 154°C revealed the inlet pressure drop to increase with increasing shearing rate, at a given entrance angle. In addition to that, the inlet pressure loss was found to decrease with increasing entrance angle from 15 to 60 °C remaining than constant. 

By assuming a behavior according to the power law for both shearing and elongation flows and applying Cogswell s law [745], the inlet pressure drop can be estimated by means of the relationship ... 

At high L D ratios, the inlet pressure drop is much lower than that in the capillary. The end effects can be neglected. 

Under these conditions, the inlet pressure drop will be lower than the theoretical one corresponding to angle 0 and the elastic component will decrease. At the same time, the viscous component increases [746], The occurrence of some high elongations strains at the capillary inlet results in the formation of some crystalline formations within the polymer melt and, hence, of some temporary networks [747],... 

Control valve inlet pressure drop of ease 1 or 2 can be calculated using Eq. (18u) or Eq. (18d) below. Eq. (1 c) is used for system without pump or compressor, while Eq. (1 Sd) ts used for systiemi has pump or compiessor. dpiO in Eq. (18c) or Eq. (18d) is the system pressure drop upstream of control valve for case 0. Use calculated dpi to adjust the case 0 control valve inlet pressure for iIk other two cases. 

Because the Super LWR is a forced convection system, increasing the inlet pressure drop increases the pressure head to force the coolant through the fuel channel. It enforces damping and hence makes the system more stable as shown in Figs. 5.32-5.34 although it does not affect the oscillation frequency of the system, as shown in Fig. 5.38. 

In case of a major problem in meeting the 3% line loss criterion, a pilot-operated relief valve can be installed with a pressure sensing tapping taken from the protected equipment. With such an installahon, it is still required to reduce the inlet pressure drop as... 

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