问题 问答题 简答题

请叙述燃气输配常用的阀门及性能。

答案

参考答案:

燃气输配常用的阀门阀门有:安全阀、截止阀、球阀、蝶阀、闸阀、止回阀、调节阀、电磁阀、旋塞阀、针型阀等。

(1)安全阀。安全阀是一种安全保护用阀,它的启闭件受外力作用下处于常闭状态,当设备或管道内的介质压力升高,超过规定值时自动开启,通过向系统外排放介质来防止管道或设备内介质压力超过规定数值,主要用于锅炉、压力容器和管道上,控制压力不超过规定值,对人身安全和设备运行起重要保护作用。

(2)截止阀。截止阀在管路中主要作切断用,具有制造工艺好,便于维修,开启高变小等优点,并且通常只有一个密封面,摩擦力比闸阀小。使用较为普遍,但由于开闭力矩较大,结构长度较长,一般公称通径都限制在DN≤200mm以下,流体阻力损失较大。因而限制了截止阀更广泛的使用。

(3)球阀。球阀的球体绕阀体中心线作旋转来达到开启、关闭的作用,在管路中主要用来做切断、分配和改变介质的流动方向,是近年来被广泛采用的一种新型阀门。目前球阀的密封面材料广泛使用塑料、密封性好,在真空系统中也已广泛用。

(4)蝶阀。蝶阀的启闭件是一个圆盘形的蝶板,在阀体内绕其自身的轴线旋转,从而达到启闭或调节功能。蝶阀全开到全关通常是小于900,它和蝶杆本身都没有自锁有力,为了蝶板的定位,要在阀杆上加装蜗轮减速器。

(5)闸阀。闸阀是常用的截断阀之一,主要用来接通或截断管路中的介质,适用于压力、温度及口径范围很大,尤其适用于中、大口径的管道。

(6)止回阀。止回阀是指依靠介质本身流动而自动开、闭阀瓣,用来防止介质倒流的阀门,根据其结构可分为升降式和旋启式两种。

(7)调节阀。调节阀根据结构分为单座型、双座型、套筒型、角形、三通型、隔膜阀、蝶阀、球阀、偏心旋转阀九个大类。前6种为直行程,后三种为角行程。这九种调节阀产品亦是最基本的产品,也称为普通产品、基型产品或标准产品。各种各样的特殊产品、专用产品都是在这九类产品的基础上改进变型出来的。

(8)针形阀。针形阀的阀芯就是一个很尖的圆锥体,好象针一样插入阀座,比其他类型的阀门能够耐受更大的压力,密封性能好,所以一般用于较小流量,较高压力的气体或者液体介质的密封,常与压力表配合使用。

(9)电磁阀。电磁阀从原理上分为三大类(即:直动式、分步童先导式),而从阀瓣结构和材料上的不同与原理上的区别又分为六个分支小类(直动膜片结构、分步重片结构、先导膜式结构、直动活塞结构、分步直动活塞结构、先导活塞结构)。

(10)旋塞阀。旋塞阀是用带通孔的塞体做为启闭件,通过塞体与阀杆的转动实现启闭动作的阀门,其结构简单,启闭迅速,流体阻力小,作为历史上最早被人们采用的阀门之一,近年来不但没再被球阀等型式的阀门所代替,反而市场呈现愈来愈火爆的趋势。

单项选择题
阅读理解

阅读理解。

     Stonehenge may have been a prehistoric health center rather than a site for observing stars or a temple

in honor of the dead, scientists said yesterday. New evidence unearthed at the World Heritage Site in more

than 40 years suggests that the monument was a place where the diseased and injured went in groups,

seeking cures.

     After a two-week dig, scientists have concluded that Stonehenge was "the ancient healthcare centre of

southern England" because of the existence of "bluestones"-the smaller columns of dolerite (辉绿岩) that

formed an earlier stone structure.

     By dating pieces of remains to around 7330BC, Tim Darvill, of Bournemouth University, and Goff

Wainwright, of the Society of Amtiquaries have found that hunter-gatherers were at the site on Salisbury

Plain 4,000 years earlier than thought. The first stage of Stonehenge, a round earthwork structure, was

built around 3000BC. Professor Wainwright added: "I did not expect the degree of complexity we discovered.

We're able to say so much more about when Stonehenge was built and why-all of which changes our

previous understanding of the monument."

     The research reveals the importance of the henge's famous bluestones. Hundreds of bluestone chips

gathered at the site have led the team to conclude that the bluestones were valued for their curing effects-the

key reason that about 80 of them, each weighing up to 4 tons and a half, were dragged more than 150 miles

from the Preseli Hills to Wiltshire. After years of research, Professors Darvill and Wainwright have

concluded that, for thousands of years, the Preseli mountain range was home to magical health centers and

holy wells.

      Even today there are those who believe in the curing powers of the springs for coughs and heart disease,

and people who use crystals and bluestones for self-curing. Radiocarbon tests have also revealed that the

construction of the original bluestone circle took place around 2300BC, three centuries later than originally

thought. Interestingly, on the same day died the "Amesbury Archer"-a sick traveler from the Swiss or

German Alps who had an infected knee-whose remains were discovered about five miles from Stonehenge.

The professors believe that he was a devoted religious person who was hoping to benefit from the curing

powers of the monument.

1. Stonehenge is recently believed to be a place for people _____.

A. to recover from poor health

B. to observe star movements

C. to hold religious ceremonies

D. to gather huge bluestones

2. What can be inferred about Stonehenge from the passage?

A. The springs could cure coughs and heart disease best.

B. The new discovery was the same as what had been expected.

C. Some huge bluestones were not produced at Stonehenge.

D. The original bluestone circle was thought to be constructed around 2000BC.

3. The sick traveler in the passage is supposed to be ______.

A. a devoted religious person from Stonehenge

B. one of the earliest discoverers of Stonehenge

C. the first explorer to test the magical power of bluestones

D. a patient trying to cure his infection at Stonehenge

4. Which of the following might be the best title for the passage?

A. Stonehenge: A New Place of Interest

B. Stonehenge: Still Making News

C. Stonehenge: Heaven for Adventurers

D. Stonehenge: Still Curing Patients