pressure from the valve that is connected to a transducer is  then converted to an electrical signal and is transmitted to  the flight deck. The torquemeter can read out in foot-pounds  of torque, percent of horsepower, or horsepower. The earlier  systems read out in psi, and the flight engineer converted this  to the correct power setting.  [Figure 10-40]  Some systems use  strain gauges to attach to the ring gear to provide an electrical  signal directly to the readout. Many of the miscellaneous gauges and devices indicate only  that a system is functioning or has failed to function. On some  aircraft, a warning light illuminates when the fuel pressure  or oil pressure is low.  The operation of the powerplant is controlled from the cockpit  or flight deck. Some installations have numerous control  handles and levers connected to the engine by rods, cables,  bellcranks, pulleys, etc. In most cases, the control handles  are conveniently mounted on quadrants in the flight deck.  Placards, or markings, are placed on the quadrant to indicate  the functions and positions of the levers. In some installations,  friction clutches are installed to hold the controls in place. The term engine instruments usually includes all instruments  required to measure and indicate the functioning of the  powerplant. The engine instruments are generally installed on  the instrument panel so that all of them can easily be observed  at one time. Manifold pressure, rpm, engine temperature, oil  temperature, CAT, and the fuel-air ratio can be controlled  by manipulating the flight deck controls. Coordinating the  movement of the controls with the instrument readings  protects against exceeding operating limits. Engine operation is usually limited by specified operating  ranges of the following: The procedures, pressures, temperatures, and rpm used  throughout this section are solely for the purpose of  illustration and do not have general application. The operating  procedures and limits used on individual makes and models  of aircraft engines vary considerably from the values shown  here. For exact information regarding a specific engine  model, consult the applicable instructions. Before starting the engine, observe the manifold pressure  gauge that should read approximate atmospheric (barometric)  pressure when the engine is not running. At sea level, this  is approximately 30 "Hg, and at fields above sea level, the  atmospheric pressure is less, depending on the height above  sea level. Also, observe all engine gauges for the correct  reading for engine off settings. Correct starting technique is an important part of engine  operation. Improper procedures often are used, because  some of the basic principles involved in engine operation  are misunderstood. Read more about typical procedures for  starting reciprocating engines in the Airframe and Powerplant  Mechanics General Handbook. Engines that have undergone overhaul or major maintenance  can have air trapped in some of the oil passages that must  be removed before the first start. This is done by pre-oiling  the engine by cranking, with the spark plugs removed, the  engine with the starter or by hand (turning) until oil pressure  is indicated. A second method is to pump oil under pressure  through the oil system using an external pump until oil comes  out of the oil outlet of the engine. Whenever a radial engine remains shut down for any  length of time beyond a few minutes, oil or fuel may drain  into the combustion chambers of the lower cylinders or  accumulate in the lower intake pipes ready to be drawn into  the cylinders when the engine starts.  [Figure 10-41]  As the  Hydraulic Lock Pre-Oiling Engine Instruments Engine Starting Reciprocating Engine Operation Warning Systems 1.  Crankshaft speed (rpm) 2.  Manifold pressure 3.  Cylinder head temperature 4. CAT 5.  Oil temperature 6.  Oil pressure 7.  Fuel pressure 8.  Fuel flow meter 9.  Fuel/air mixture setting 0 5 10 15 20 25 30 35 40 45 50 TORQUE FTLB x100 Figure 10-40.  Torquemeter readout.  10-25