作者：Brendan Casey
充气式蓄能器在现代液压系统普遍存在，它们的执行功能，包括能量储备和保存、泄漏和热量补偿、吸收震动、和能量恢复。
蓄能器在液压系统运行方面有很多好处，可以提供多年无故障运行服务，它们也是维护对象。
例如，正确的充气压力能保持合适的功能和适宜的服务寿命。还有定期检测、测试和法律规定需要的合格证（蓄能器也是压力容器）。
蓄能器类型
你遇到液压系统的充气式蓄能器有三种类型：气囊式、活塞式和隔膜式。
大多数常用蓄能器是气囊式的，气囊式蓄能器有快速响应性能（小于25毫秒），最大气体压缩比为4：1，最大流量可达15L/S（4加仑/S），虽然大流量型可以达到38L/s是可行的。气囊式蓄能器也有好的耐污性，它们几乎不受液压液体中固体颗粒污染物的影响。
活塞蓄能器，另一方面，可以达到更高的压缩比（达比10：1），流量达到215L/s。不同于气囊式蓄能器能在任意位置安装。
但是，活塞式蓄能器比气囊式蓄能大需要液体有更高的清洁度等级，较慢的响应时间（超过25毫秒）=特别是在低压状态显示滞后。这主要是活塞密封的静态摩擦下会被战胜，和活塞质量造成的可能的加速和减速。
隔膜式的蓄能器有大多数气囊式蓄能器的好处，便是它的气体压缩比可以达到8：1。它们被限制用在小容量蓄能器，它们的性能有时会受到气体通过隔膜渗漏的影响。
维护注意事项
当给气囊式和隔膜式蓄能器充气时，氮气经常要求非常慢。假如高压氮气允许进入气囊时快速地扩张，它将导致把气囊的聚合物材料变冷到某部位点立即地易碎失效发生。快速充气也会将气囊挤入油端锥形阀下面，导致气囊被切。如果预充气压力过高或者最小系统压力变小而预充气压力没有做相应减少，蓄能器的运行将受影响和导致损坏的结果。
气囊式蓄能器过分的预充气会在泄压时把气囊卡进装配的锥形阀里，导致锥形阀或气囊损坏。这是气囊失效的基本原因。
低压或者没有预充气也能是气囊式蓄能器过频波动。结果是气囊在系统压力下在壳体顶部起皱损坏。这将导致气囊被气囊被气阀挤入或被刺破。在这种情况下，仅仅需要一个循环就会破坏气囊。
一样的，过高或者过低的预充气压力会导致活塞蓄能器的活塞到达行程末端的底部，损坏活塞和它的密封。好消息是，假如这发生，一个听的见的警示将产生。即将活塞蓄能器能被不合格的充气损坏，它们还是比气囊式蓄能器更可以让人容忍。
坚持标准
蓄能器是压力容器，从生产、测试和验证都要按照法定的标准，在美国，例如，相关标准是ASME锅炉和压力容器编号VIII,1级。
所有按照这些标准制造的压力容器，要考虑限定的服务寿命建立在正常运行一定压力循环次数上。典型的液压蓄能器设计寿命是12年。
在许多管辖内容，定期检查和再检验是需要的。这个特别的应用是给相关大容积和在高的工作压力下的液压蓄能器。检查可能需要在预先确定的时间间隔内（即每隔2年、5年或10年）或被认为已经达到了一定比例的可用设计寿命。
根据蓄能器的容量和压力等级，换发新证可能涉及一个或多个以下内容：目视检查、超声波测厚测试和/或静态水压测试。
你责任重大
所以如果你负责包含一个蓄能器的液压设备，你要熟悉应用于你的工作场所的有关规定。和你的其他的液压设备部件一们，你有责任保证你的蓄能器的合理维护和安全使用。（中国设备管理协会流体污染控制中心：李海军翻译，本翻译仅为学习交流，版权归Noria公司所有）
原文：
Advice For Maintaining HydraulicAccumulators
Gas-charged accumulators are ubiquitous onmodern hydraulic systems. They carry out numerous functions, which includeenergy storage and reserve, leakage and thermal compensation, shock absorption,and energy recovery.
While accumulators present a number ofadvantages in hydraulic system operation and can provide many years oftrouble-free service, they are a maintenance item.
For example, the correct gas pre-chargepressure must be maintained for proper functioning and optimum service life.Also, periodic inspection, testing and certification can be required by law-accumulatorsare pressure vessels after all.
Accumulator Types
The three types of gas-charged accumulatorsyou’ll encounter on hydraulic systems are bladder, piston and diaphragm.
The most popular of these is the bladdertype. Bladder accumulators feature fast response (less than 25 milliseconds), amaximum gas compression ratio of around 4:1 and a maximum flow rate of 15liters (4 gallons) per second are available. Bladder accumulators also havegood dirt tolerance; they are mostly popular of these is the bladder type.Bladder accumulators also have good dirt tolerance; they are mostly unaffectedby particle contamination in the hydraulic fluid.
Piston accumulators, on the other hand, canhandle much higher gas compression ratios (up to 10:1) and flow rates as highas 215 liters (57 gallons) per second. Unlike bladder accumulators, whosepreferred mounting position is vertical to prevent the possibility of fluidgetting trapped between the bladder and the shell, piston accumulators can bemounted in any position.
But, piston accumulators also require ahigher level of fluid cleanliness than bladder units, have slower responsetimes (greater than 25 milliseconds)-especially at lower pressures- and exhibithysteresis. This is explained by the static friction of the piston seal whichhas to be overcome, and the necessary acceleration and deceleration of thepiston mass.
Diaphragm accumulators have most of theadvantages of bladder-type units but can handle gas compression ration up to8:1. They are limited to smaller volumes, and their performance can sometimesbe affected by gas permeation across the diaphragm.
Maintenance Considerations
When charging the gas end of a bladder ofdiaphragm accumulator, the nitrogen gas should always be admitted very slowly. Ifthe high-pressure nitrogen is allowed to expand rapidly as if enters thebladder, it can chill the bladder’s polymeric material to the point whereimmediate brittle failure occurs. Rapid pre-charging can also force the bladderunderneath the poppet at the oil-end, causing it to be cut. If pre-chargepressure is too high or minimum system pressure is reduced without acorresponding reduction in pre-charge pressure, the operation of theaccumulator will be affected and damage may also result.
Excessive pre-charge of a bladderaccumulator can drive the bladder into the poppet assembly during discharge,causing damage to the poppet assembly and/or the bladder. This is a commoncause of bladder failure.
Low or no pre-charge also can have drasticconsequences for bladder accumulators. It can result in the bladder beingcrushed into the top of the shell by system pressure. This can cause thebladder to extrude into or be puncture by the gas valve. In this scenario, onlyone such cycle is required to destroy the bladder.
Similarly, excessively high or lowpre-charge of a piston accumulator can cause the piston to bottom out at theend of its stroke, resulting in damaged to the piston and its seal. The goodnews is that, if this happens, an audible warning will result. Even thoughpiston accumulators can be damaged by improper charging. They are much moretolerant of it than bladder accumulators.
Held to Standards
Accumulators are pressure vessels and assuch are manufactured, tested and certified according to statutory standards.In the United States, for example, the relevant standard is the ASME Boiler& Pressure Vessel Code VIII, Division 1.
All pressure vessels manufactured to thesestandards are considered to have a finite service life depending on the numberof pressure cycles experienced during normal operation. The typical design lifefor a hydraulic accumulator is 12 years.
In many jurisdictions, periodic inspectionand recertification is required. This particularly applies to hydraulicaccumulators which have relatively large volumes and operate at high workingpressures. Inspection may be required atpredetermined intervals (i.e. every two, five or 10 years) or when a certainpercentage of usable design life is deemed to have been reached.
Depending on the volume and pressure ratingof the accumulator, recertification may involve one or more of the following:visual inspection, ultrasonic thickness testing and/or hydrostatic pressuretesting.
You ’are Responsible
So if you’re responsible for hydraulicequipment which incorporates an accumulator, familiarize yourself with therelevant regulations that apply in your locale.
And along with every other component onyour hydraulic machines, it’s your responsibility to make sure all accumulatorsare properly maintained and safe to use.（Brendan Casey）
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