Valve will not open

Users are warned that an ordinary spring loaded safety relief valve will not open at its set pressure if back pressure builds up in the space between the valve and rupture disk. A specially designed valve is required, such as a diaphragm valve or a valve equipped with a bellows above the disk. 

If the high side is being tested, the low side should be vented to the atmosphere, in case there is any leakage between them which could bring excessive pressure onto the low side. It may be necessary to remove relief valves. Other valves within the circuit will have to be open or closed as necessary to obtain the test pressure. Servo-operated valves will not open on a dead circuit, and must be opened mechanically. 

Pressure safety relief valves will not open except on demand... 

P2 is less than l.OOX 10 torr, so the valve will not open. 

The valves under the individual collecting hoppers open either in a predetermined sequence at certain intervals or in response to the level of the material in the hoppers, which operates a control system. In the latter case, however, the valves must be interlocked so as to make sure that several valves will not open simultaneously and overload the clinker handling equipment. 

They are not recommended for dirty or fouling services, because of plugging of the pilot valve and small-bore pressure-sensing lines. If the pilot valve or pilot cormections become fouled, the valve will automatically open. In special cases where fouling is a function of entrained solids, this limitation may be countered by the use of a nonflowing pilot valve and a pilot line filter. With a nonflowing pilot valve, there is no normal flow in the pilot system and therefore solids entrainment is reduced. 

The set pressure tolerances of pressure relief valves are not to exceed +2 psi for pressures up to and including 70 psig and +3% for pressures above 70 psig. Indirect operation of safety valves, for example, by pilot valve, is not acceptable unless the primary unloading valve will automatically open at not over the set pressure and will operate fully in accordance with design relieving capacity conditions if some essential part of the pilot or auxiliary device should fail [1]. 

Catalyst circulation can also be limited by mechanical problems with the slide/plug valves. They may have limited travel or will not open fully. This is indicated by the lack of response when an adjustment is made. The differential pressure and the flow will not change. Troubleshooting the valves is a function of the valve design and the vendor will supply troubleshooting information,... 

If we use a controller with positive gain (+KC), the controller output increases as the liquid level drops. We can only reduce the flow if we use an air-to-close valve (-Kv). In the case of a power outage, the valve will stay open. This fail-open valve can drain the entire tank, an event that we may not want to happen. 

Figure 1-7 presents the causes of losses for the largest chemical accidents. By far the largest cause of loss in a chemical plant is due to mechanical failure. Failures of this type are usually due to a problem with maintenance. Pumps, valves, and control equipment will fail if not properly maintained. The second largest cause is operator error. For example, valves are not opened or closed in the proper sequence or reactants are not charged to a reactor in the correct order. Process upsets caused by, for example, power or cooling water failures account for 11 % of the losses. 

For a conventional spring-operated relief, the valve opens based on the pressure drop across the valve seat that is, the set pressure is proportional to the pressure drop across the seat. Thus, if the backpressure downstream of the valve increases, the set pressure will increase and the valve may not open at the correct pressure. In addition, the flow through the conventional relief is proportional to the difference in pressure across the seat. The flow through the relief, therefore, is reduced as the backpressure increases. 

The in vivo and in vitro pressure gradient information clearly show that the Hancock porcine valves are moderately to highly stenotic, especially in the smaller sizes. Patients with these valves will not be able to lead very active lives due to the large gradients across these valves under exercise conditions. The stenotic nature of the valve is in part due to the asymmetric and inadequate opening of the three leaflets. The jet type flow observed in the flow visualization studies could cause damage to the aortic or ventricular wall if the jet impinges on these walls. As stated previously the velocity and shear fields... 

IDENTIFICATION OF PROTECTION. Protection reduces the probability of the consequence occurring given that the cause has occurred. There are two key questions to ask when reviewing the protection portion of a PrHA. First, is the protection capable of preventing the consequence if it functions correctly Second, will the protection function, given the cause For example, a normally open electric solenoid valve will not close after loss of electrical power and, therefore, cannot function as protection under that circumstance. A motor-operated valve also will not operate after loss of electrical power. However, a normally closed electric solenoid valve will automatically close upon loss of power. 

Relief valves are designed to respond automatically to sudden increases in pressure. A relief valve opens at a predetermined pressure. In a relief valve, a disc is held in place by a spring that will not open until system pressure exceeds its operating limits. Tremendous pressures can be generated in process units. When a system overpressurizes, safety valves respond to allow excess pressure to be vented to the flare header or atmosphere. This prevents damage to equipment and personnel. Relief valves are designed to open slowly, and thus are best for pressurized liquid service. They do not respond well in gas service, where quicker pressure reduction is needed. 

Now the valve is open, and the pressure force is acting over a larger area. This means that the valve will not close when the pressme falls to the set pressure (because the pressure is acting on a larger area). The disk will fall back when the vessel or system pressure falls a little below the set pressure. The difference between the set pressure and closing pressme is called blowdown, which is an important design criterion. 

Check valve flapper pin is worn, and flapper will not swing open. 

Step 7 Calculate the differential in Ae One PRT eontrol objeetive is to maintain the differential pressure between the regenerator and the reaetor stripper. At the time of the breaker opening, it is assumed that the reaetor stripper pressure will not vary. Therefore, to keep the differential pressure eonstant, the regenerator pressure needs to also remain eonstant. Eor the expander, this means that must remain eonstant. To keep P eonstant, the mass flow before and after the breaker opening must remain eonstant (Equations 7-7 and 7-8). This implies that whatever mass flow is redueed on the inlet valve must be rerouted over the bypass valve. 

When a pump has a motor drive, the process engineer must verify that the motor will not overload from extreme process changes. The horsepower for a centrifugal pump increases with flow. If the control valve in the discharge line fully opens or an operator opens the control valve bypass, the pump will tend to run out on its curve, giving more flow and requiring more... 

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