Poppet valve

A poppet valve is a valve used to control the timing and quantity of gas or vapor flow into an engine. It consists of a hole round or oval, a tapered plug a disk shape on the end of a shaft called a valve stem; the portion of the hole where the plug meets with it is called the "seat" or "valve seat". The shaft guides the plug portion by sliding through a valve guide. In exhaust applications a pressure differential helps to seal the valve and in intake valves a pressure differential helps open it; the poppet valve was most invented in 1833 by E. A. G. Young of the Newcastle and Frenchtown Railroad. Young patented his idea; the word poppet shares etymology with "puppet": it is from the Middle English popet, from Middle French poupette, a diminutive of poupée. The use of the word poppet to describe a valve comes from the same word applied to marionettes, like the poppet valve, move bodily in response to remote motion transmitted linearly. In the past, "puppet valve" was a synonym for poppet valve; the valve stem moves up and down inside the passage called a guide, fitted in the engine-block.

The head of the valve called valve face, is ground to a 45-degree angle, so as to fit properly on the valve seat in the block and prevent leakage The poppet valve is fundamentally different from slide and oscillating valves. The main advantage of the poppet valve is that it has no movement on the seat, thus requiring no lubrication. In most cases it is beneficial to have a "balanced poppet" in a direct-acting valve. Less force is needed to move the poppet because all forces on the poppet are nullified by equal and opposite forces; the solenoid coil has to counteract only the spring forcePoppet valves are used in many industrial processes, from controlling the flow of milk to isolating sterile air in the semiconductor industry. However, they are most well known for their use in internal combustion and steam engines, as described below. Presta and Schrader valves used on pneumatic tyres are examples of poppet valves; the Presta valve has no spring and relies on a pressure differential for opening and closing while being inflated.

Poppet valves are employed extensively in the launching of torpedoes from submarines. Many systems use compressed air to expel the torpedo from the tube, the poppet valve recovers a large quantity of this air in order to reduce the tell-tale cloud of bubbles that might otherwise betray the boat's submerged position. Poppet valves are used in most reciprocating engines to open and close the intake and exhaust ports in the cylinder head; the valve is a flat disk of metal with a long rod known as the "valve stem" attached to one side. In early internal combustion engines it was common that the inlet valve was automatic, i.e. opened by the suction in the engine and returned by a light spring. The exhaust valve had to be mechanically driven to open it against the pressure in the cylinder. Use of automatic valves simplified the mechanism, but "valve float" limited the speed at which the engine could run, by about 1905 mechanically operated inlet valves were adopted for vehicle engines. Mechanical operation is by pressing on the end of the valve stem, with a spring being used to return the valve to the closed position.

At high revolutions per minute, the inertia of the spring means it cannot respond enough to return the valve to its seat between cycles, leading to valve float known as "valve bounce". In this situation desmodromic valves can be used, being closed by a positive mechanical action instead of by a spring, are able to cycle at the high speeds required in, for instance and auto racing engines; the engine operates the valves by pushing on the stems with cams and cam followers. The shape and position of the cam determines the valve lift and when and how the valve is opened; the cams are placed on a fixed camshaft, geared to the crankshaft, running at half crankshaft speed in a four-stroke engine. On high-performance engines, the camshaft is movable and the cams have a varying height so, by axially moving the camshaft in relation with the engine RPM, the valve lift varies. See variable valve timing. For certain applications the valve stem and disk are made of different steel alloys, or the valve stem may be hollow and filled with sodium to improve heat transport and transfer.

Although a better heat conductor, an aluminium cylinder head requires steel valve seat inserts, where a cast iron cylinder head would have employed integral valve seats in the past. Because the valve stem extends into lubrication in the cam chamber, it must be sealed against blow-by to prevent cylinder gases from escaping into the crankcase though the stem to valve clearance is small 0.04-0.06 mm, so a rubber lip-type seal is used to ensure that excessive oil is not drawn in from the crankcase on the induction stroke, that exhaust gas does not enter the crankcase on the exhaust stroke. Worn valve guides and/or defective oil seals can be diagnosed by a puff of blue smoke from the exhaust pipe on releasing the accelerator pedal after allowing the engine to overrun, when there is high manifold vacuum; such a condition occurs. In multi-valve engines, the conventional two-valves-per-cylinder setup is complemented by a minimum of an extra intake valve (three-valve cylinder head

Harlem Renaissance theater companies

A number of theatre companies are associated with the Harlem Renaissance. Anita Bush, a pioneer in African American theater, began an acting company after seeing a show at the Lincoln Theater in Harlem, she wanted an all-Black group that performed Broadway plays, to combat the popular "racial stereotypes of African Americans as singers and slapstick comedians." According to Bush, she wanted to prove. They were called the Bush Players. After performing at the Lincoln Theater for two years, the owner, Marie Downs, wanted to change their name to the Lincoln Players. Anita took her company to the rival theater, The Lafayette Theatre. In 1916, due to financial difficulties, Bush sold her company to the theater. One of the actors, Charles S. Gilpin, took over the players and helped establish the Lafayette Players Stock Company, which became the first legitimate Black stock company in Harlem; that same year Robert Levy, an American Jew, became involved with the Lafayette Players through the formation of the Quality Amusement Corporation, which managed both the theater and the acting troupe.

Levy used the talents of the players in the movies he produced. Reol Productions Corporation had a goal to product high-class pictures with colored actors, which created continuous employment for Black performers; the company consisted of only black actors who were cast as serious dramatic roles—something, unheard of at the time. White playwrights, who intended to have white actors playing them, wrote many of these roles; this allowed serious black actors transcend the stereotyped and comedic roles, which they were expected to play. The Lafayette Players began performing for exclusively Black audiences; the plays they would perform were shows that were popular in the white theater repertory as well as the classics. Some examples of these are performances: Madame X, Dr. Jekyll and Mr. Hyde, Shakespeare's Macbeth, directed by Orson Welles; the Players performed anything, being done on Broadway. They performed short plays, shortened versions of popular Broadway success'—most which were melodramatic.

Sometimes they would perform musicals like Shuffle Along. Some Harlem figures, like W. E. B. Du Bois, opposed this choice of materials. By 1924, the Players were divided up into four different groups; the original cast stayed at the Lafayette Theater in Harlem. A new group was created in Chicago. Two traveling groups formed—one that traveled throughout the South, one along the East coast; these groups only played in theaters. The groups, performed over two hundred plays that had never been performed by a black cast, their job was not only to make a point against the mainstream theater and society, but to educate the Black audience around the country. Some actors who were cast in the Lafayette Players: Edna Morton, Lawrence Chenault, Canada Lee, Rose McClendon, Oscar Micheaux, Clarence Muse, Charles S. Gilpin; the arranger James P. Johnson was involved for a while as well as the famous director Edgar Forrest; when the Depression started taking its toll, the performers were one of the first to get hit.

In 1928, a white company relocated them to Los Angeles, California. Here they performed till 1932. Ida Anderson got her start working for Anita Bush and after two years in the Lafayette Players she started her own players; the Ida Anderson Players got hired at the Lincoln Theater. The Anderson Players resided there till 1928. After her termination, the troupe was renamed The Lincoln Players; when W. E. B. Du Bois saw a production of the Negro Players performing Ridgely Torrence's Three Plays for a Negro Theater in 1917, it influenced him to write, "The present spiritual production in the souls of Black folk is going to give American stage a drama that will lift it above silly songs and leg shows." When the Circle for Negro War Relief had developed a branch in New York City, New York, they established a theater company named the Players' Guild. The Players' Guild had several performances during the 1920s at the local Harlem YMCA. One of these productions helped the actor Paul Robeson rise to stardom.

After the Guild made the YMCA their home, the place became a new venue for Black drama. The Guild was admired for creating a substitute from the cheap musical comedy and melodramatic works that were taking over Harlem theaters; the Acme Players developed out of a performance by the National Urban League at the Lafayette Theater in 1922. In May 1923, under the direction of a white woman named Anne Wolter, the Players gave a performance at the Harlem YMCA. Here they performed two of Frank Wilson's short plays -- The Heartbreaker; when Wolter realized the Players' success, she developed the National Ethiopian Art Theater, which became a school. Both, the Acme Players and the Ethiopian Art Theater furthered the three goals of creating a black theater, improve black actors, performing black drama; the National Ethiopian Art Theater grew out of the success of the Acme Players. It was a short-lived cast and a school the encouraged playwriting and dramatic performances by African Americans; the teachers at the school included the organizers of the theater.

The first public performance put on by NEAT was on June 19, 1924. The performance included choral dance numbers. Another known performance of theirs was at the Lafayette Theater, where they performed three one-act plays; the school was disbanded in 1925. In 1925, W. E. B. Du Bois and Regina Anderson co-founded the Krigwa Players fo

Hedwig of Brandenburg, Duchess of Brunswick-Wolfenb├╝ttel

Hedwig of Brandenburg, a member of the Hohenzollern dynasty, was Duchess of Brunswick-Lüneburg and Princess of Brunswick-Wolfenbüttel from 1568 to 1589, by her marriage with the Welf duke Julius. Born at the City Palace in Cölln, Hedwig was a younger daughter of Elector Joachim II Hector of Brandenburg from his second marriage with Hedwig Jagiellon, a daughter of King Sigismund I of Poland, her elder sister Elizabeth Magdalena was married to Duke Francis Otto of Brunswick-Lüneburg in 1559. One year on 25 February 1560, Hedwig was married in Cölln on the Spree river to the Welf prince Julius of Brunswick-Lüneburg; the couple had met at the Küstrin court of Margrave John of Brandenburg, where Julius had fled from his wayward father, Duke Henry V After Julius had reconciled with his father, who had agreed only reluctantly to the marriage of his son with a Protestant princess, the couple received the castles of Hessen and Schladen as residences. As Julius's elder brothers had been killed in the 1553 Battle of Sievershausen, Duke Henry V was alleged to have appeared at Hessen Castle and let himself into the room of his daughter-in-law, took her newborn son Henry Julius from the cradle and exclaimed: You'll now have to be my beloved son!.

In 1568 Julius succeeded his father as ruling Prince of Brunswick-Wolfenbüttel. He turned out to be a capable ruler. Hedwig was described with preference for domestic activities. In 1598, the theologician Stephan Prätorius dedicated his book Der Witwen Trost to Hedwig. From her marriage to Julius, Hedwig had following children: Sophie Hedwig married in 1577 Duke Ernest Louis of Pomerania-Wolgast Henry Julius, Duke of Brunswick-Wolfenbüttel, married: in 1585, Princess Dorothea of Saxony in 1590, Princess Elizabeth of Denmark Maria married in 1582, Duke Francis II of Saxe-Lauenburg Elisabeth, married in 1583 to Count Adolf XI of Holstein-Schauenburg in 1604 to Duke Christopher of Brunswick-Harburg Philip Sigismund, Bishop of Osnabrück and Verden Margaret Joachim Charles Sabine Catharina Dorothea Augusta, Abbess of Gandersheim Julius Augustus, abbot of Michaelstein Abbey Hedwig married in 1621 Duke Otto III of Brunswick-Harburg Inge Mager: Die Konkordienformel im Fürstentum Braunschweig-Wolfenbüttel, Vandenhoeck & Ruprecht, 1993, p. 22 ff Media related to Hedwig of Brandenburg at Wikimedia Commons