Fuel Control Valves

Flow hysteresis was a major challenge as the prototype proportional solenoid valves were being developed. The earliest version of the proportional solenoid valves produced the flow curve shown in Fig. 17.4a, having a large hysteresis 

A PC-based controller was developed to operate the valves for fuel flow modulation in the various zones. The valve hardware and controller were bench tested in a jet-fuel wet-bench test facility to verify valve performance and controller effectiveness. Valve flow tests indicate stable and repeatable valve operation over the range of flow conditions tested. The valve flow curves demonstrated acceptable proportionality at lower mass flows, but became slightly nonlinear at higher mass flow conditions as illustrated by Fig. 17.6. 

Some variability in the flow curves of the different valves is also noted in Fig. 17.6. A level of discrepancy is expected for the first generation, prototype valve, and the variability would be reduced with changes in the manufacturing process for production valves. For rig testing, the variability can be accommodated with the computer-based control system. 

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Slowly open the pilot fuel control valve to the manufacturer-specified pilof fuel pressure visually confirm sfable ignition of the pilot flame. 

Slowly open the main burner fuel control valve to supply the burner with the manufacturer-specified ignition fuel pressure visually confirm stable ignition of the main burner flame. 

The chemical composition and quality of the fuel will to some extent influence the power output. However, it is usually the case that more or less fuel has to be supplied by the fuel control valve for a given throughput of combustion air. Hence it is usually possible to obtain the declared normal rating from the machine, but attention has to be given to the supply of the fuel. In extreme cases the profile of the fuel control valve may require modification so that adequate feedback control is maintained over the full range of power output. The appropriate derating factor is usually 100%, i.e. no derating. 

The fuel gas to a fired heater is controlled by a BPCS control function (function TIC-1), which throttles a fuel control valve, CV-1, as shown in Figure F-3. A hazard analysis was performed to identify process hazards and to determine whether the safeguards were sufficient to mitigate the process hazards. The team determined that when the heater was firing hard, a low-pass flow through the tubes could result in a high firebox temperature with the potential for tube rupture, furnace fire and structural damage to the furnace. 

To explore dynamic behaviour, as an example, we will use a simple fired heater as shown in Figure 2.1. It has no automatic controls in place and the minimum of instrumentation - a temperature indicator (Tl) and a fuel control valve. The aim is to ultimately commission a temperature controller which will use the temperature as its process variable (PV) and the fuel valve position as it manipulated variable (MV). 

The key components in the fuel vapor control system include the fuel tank, vapor vent valves, vapor control valve, vapor tubing, the activated carbon canister, and the engine vapor management valve (VMV) [25,26], During normal vehicle operation, fuel tank vapor pressure is relieved through the use of vapor vent valves installed in the vapor dome of the fuel tank. The vent valves are designed to allow for the flow of fuel vapor from the tank, and to assure that liquid fuel does not pass through the valve. 

The vapor vent valves are connected to the tank vapor control valve, and ultimately to the carbon canister by tubing that is resistant to swelling in the presence of fuel vapors. The tubing material must also have a low HC permeation rate, so that the evaporative emissions are not increased due to release of HC molecules. The tank vapor control valve connects the carbon canister to two fuel tank vapor sources the vapor vent valve lines and a refueling vent tube. 

Fuel system components involved in the refueling process include the fuel tank, filler pipe, filler cap, vapor control valve, liquid-vapor discriminator (LVD) valve, and the carbon canister [27,28]. During vehicle refueling, which is monitored during the integrated refueling test as outlined in Fig. 1, the following operations occur in the evaporative emission control system ... 

Abnormal Process Heat Input - The required capacity is the maximum vapor generation rate at PR valve relieving conditions, including any noncondensibles produced from overheating, less the normal condensation or vapor outflow rate. In every case, one should consider the potential behavior of a system and each of its components. For example, the fuel or heating medium control valve or the mbe heat transfer may be the limiting consideration. Consistent with the practice... 

Car-Sealed Closed Valve - In certain cases it may be advantageous to use car sealed closed valves, such as in a bypass around a fuel gas control valve used for furnace flameout protection. The bypass is provided so that the automatic shutdown system can be periodically checked for operation. Where CSC valves are used for other purposes, they are also limited to appUcations where inadvertent opening of the CSC valve would not overpressure the equipment by more than 1.5 times design pressure. 

The mechanic, who had done the job many times before, took the cover off the back of B recorder, the one on the left behind the panel (Figure 3-3). and disconnected one of the leads. The effect was the same as if the recorder had registered a high temperature. The controller closed the fuel gas valve, shutting down the furnace and the rest of the plant. 

Fig. 26. Control scheme b 7i, average temperature at air inlets Tz, combustion air temperature S, desired combustion air temperature Pt, position of fuel gas valve. Control goal constant temperature above coils.

High furnace stack-gas temperature should pinch the fuel gas control valve. 

Current efforts are focusing on optimizing the carbon monoxide removal reactor and developing a system prototype using commercially available pumps, blowers, fuel cells, valves, and controllers.In addition, durability testing along with thermal cycling needs to be done. 

In order to overcome the difficulties associated with the non-choked fuel-flow system and the fixed fuel-flow system, a variable fuel-flow system is introduced the fuel gas produced in a gas generator is injected into a ramburner. The fuel-flow rate is controlled by a control valve attached to the choked nozzle according to the airflow rate induced into the ramburner. An optimized mixture ratio of fuel and air, which is dependent on the flight altitude and flight velocity, is obtained by modulating the combustion rate of the gas-generating pyrolant When a variable fuel-flow-rate system is attached to the choked nozzle of the gas generator, the fuel-flow rate is altered in order to obtain an optimized combustible gas in the ramburner. This class of ducted rockets is termed variable fuel-flow ducted rockets or VFDR . 

An obvious method of controlling the capacity of a compressor is to vary the speed. This method is applicable to units driven by variable-speed drivers such as steam pistons, steam turbines, gas engines, diesel engines, etc. In these cases the regulator actuates the steam-admission or fuel-admission valve on the compressor driver and thus controls the speed. 

I once tried to increase the flow of jet fuel from a crude distillation column by opening the draw-off, flow-control valve. Opening the valve from 30 to 100 percent did not increase the flow of jet fuel at all. This is a sure sign of nozzle exit loss—or cavitation limits. To prove my point, I increased the level of liquid in the draw-off sump from 2 to 4 ft. Since flow is proportional to velocity and head is proportional to (veloc-... 

If we have the furnace on automatic temperature control while we are not using enough combustion air, and if the control valve on the fuel gas then opens to allow more fuel to the burners in order to either maintain or perhaps increase the furnace outlet temperature, the extra fuel will not burn efficiently. In fact, the extra fuel is likely to reduce the heater or furnace outlet temperature rather than increase or maintain it, as there is already a shortage of air and it cannot bum properly and tends to cool the firebox. The automatic temperature controller... 

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