英語聽力文摘 水塔物理學(xué)原理

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水塔，一般居民區(qū)里蓄水作用，有些還是水廠生產(chǎn)工藝的一個重要組成部分，用于保持和調(diào)節(jié)給水管網(wǎng)中的水量和水壓。主要由水柜、基礎(chǔ)和連接兩者的支筒或支架組成。在工業(yè)與民用建筑中，水塔是一種比較常見而又特殊的建筑物。它的施工需要特別精心和講究技藝，如果施工質(zhì)量不好，輕則造成永久性滲漏水，重則報廢不能使用。

Water towers take advantage of the force of gravity to provide pressure for the water they contain. Every vertical foot adds point-four-three pounds per square inch to the water pressure. Towns usually keep their water pressure between fifty and one-hundred pounds per square inch, so a simple equation tells them how high to build the tower. And since a typical tower contains a full day’s worth of water, the force of gravity can maintain the hydrostatic pressure of the water system even when the power goes out.

水塔其實是利用重力給蓄水提供壓力，每增加一英尺高度，水壓增加0.43磅/平方英寸。城鎮(zhèn)所需水壓在50-100磅/平方英寸之間，簡單換算一下就知道水塔需要建多高。普通水塔儲蓄一整天的用水，由此，即便在停電的情況下，重力作用仍能保持供水系統(tǒng)的靜水壓力。

Actually they serve an important day-to-day purpose as well. A city’s water usage varies throughout the day, usually peaking in the early morning when many people are showering and washing. Water usage during this time can be four or five times higher than during other parts of the day. To maintain water pressure during peak hours of the day, a city could invest in a very powerful pump, but this would be expensive and wasteful, since its capacity would go unused for most of the day.

事實上，水塔在日常用途中也起著十分重要的作用。城市一天用水量變化不斷，通常情況下，早晨人們洗漱的時候達(dá)到高峰值。這個時段的耗水量是一天中其他時段的4到5倍。為了在高峰時段維持水壓，城市需要投資購買大功率的水泵，然而水泵在其他時段卻派不上用場，因此會浪費(fèi)的昂貴品。

Let me guess，instead, the city draws on the water tower’s supply of water during these hours of high demand.

我猜想，在高需求時段，城市利用的是水塔的供水。

That's right, the water tower and pumps work together to keep the water pressure stable throughout the day.

的確如此，水塔和水泵協(xié)力保持水壓在一天中持續(xù)穩(wěn)定。

NOTES

1.pounds per square inch:磅/平方英寸，縮寫為PSI，英制壓力單位，歐美等國家習(xí)慣使用psi作單位，在很多進(jìn)口的壓力容器安全閥上采用這種標(biāo)示。

在中國，壓力用“公斤”描述(而不是“斤”)，體單位是“kg/cm^2”,一公斤壓力就是一公斤的力作用在一個平方厘米上。而在國外常用的單位是“Psi”，具體單位是“lb/in2”, 就是“磅/平方英寸”，這個單位就像華氏溫標(biāo)(F )。此外，還有Pa(帕斯卡，一牛頓作用在一平方米上)，KPa，Mpa，Bar，毫米水柱，毫米汞柱等壓力單位。

1兆帕(MPa)=145磅/英寸2(psi)=10.2公斤/平方厘米=10巴(bar)=9.8大氣壓(atm)

2.hydrostatic pressure：靜水壓力。