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选择计量齿轮泵的7个技巧


更新日期:2020-10-27 20:45:27
关键词: 计量齿轮泵 齿轮泵选型

在外部齿轮泵的一般分类中,精密齿轮计量泵是一个专门的子集,在广泛的应用和工艺流体条件下提供准确、可靠和无脉冲的计量性能。


虽然许多齿轮泵的应用是为了简单地输送粘性液体而设计的,但其他一些产品的生产公差非常小,可以承受更高的压力和精确的流量,满足精密计量应用的要求。它们与用于输送应用的齿轮泵的不同之处在于,内部操作间隙更紧密,最大限度地减少内部流体滑移,并允许测量和输送高度精确的流体量。由于其极端接近的公差和较小的齿轮尺寸,这些泵能够在压力为10,000 psi,温度为- 40f到950 F的情况下,流量低至0.5立方厘米/分钟。在流程行业中,没有什么比确保流程本身的完整性更关键的任务了。支持这些工艺的泵系统必须经过独特的设计和配置,以符合这种独特的工艺。近公差精密齿轮计量泵在计量应用提供准确的输送,可靠的服务,并具有几乎无脉冲流体输送性能。

选择计量齿轮泵的7个技巧

依靠精密齿轮计量泵进行计量、混合和喷涂的应用包括化学品、挤压塑料、纤维纺丝、油漆、粘合剂和密封剂,或其他支持特定工艺操作或最终产品的添加剂。


在这些情况下,由于脉动流引起的流量变化要么会完全破坏最终产品,要么会生产出不符合规格的产品,从而导致生产力损失、返工增加和过多的产品浪费——所有这些最终结果都增加了制造商的成本。


精密齿轮计量泵可以解决的挑战包括:


•过度喷涂/过度配药导致物料浪费过多,增加了制造成本


•过量添加添加剂以解释剂量不足导致的额外成本和对产品吸引力的影响


•难以控制挤出机的变化,如压力波动、粘度不一致和密度变化


•喷漆设备应用中的压力和体积变化效率低下,影响生产线的质量和生产率


•过度添加昂贵的工艺化学品,以防止用量不足,影响成品质量


•价格昂贵的添加剂的不规则、脉动输送

选择计量齿轮泵的7个技巧

齿轮泵具有很高的耐磨性和尺寸稳定性,即使在极端的流体温度、压力、粘度和磨料或腐蚀性成分下也是如此。可容纳粘度达200万厘泊(cP)的产品。


准确的输送液体的体积输出是计量的,并根据齿轮齿的大小和它们旋转的速度,以最小的脉动,以精确的恒定速度移动。精密计量齿轮泵可以实现最紧密的泵送间隙,以微米计量,以最大限度地减少流体滑移。


齿轮齿尖和侧壁之间的间隙可以低至0.00015英寸(0.0031毫米)。这些间隙比一张普通的纸还要薄20倍。


许多零件的制造公差可能达到正负50万分之一英寸,表面光洁度可能达到4微英寸或更好。一个连续的,无脉流的分配或剂量的结果,因为齿轮泵移动许多小腔每一转。


即使在运行速度、压力和温度变化时,也可以保持持续的线性流量。驱动系统和闭环速度控制器可以保持速度精度在0.1%的水平。


可靠的服务计量齿轮泵可以用多种不锈钢制成,用于腐蚀或卫生应用,但通常用硬化的工具钢制成,用于研磨应用。由于计量齿轮泵坚固的结构和有限的活动部件,其维护费用通常比其他技术低得多。在许多情况下,只有三个运动部件——传动轴、驱动齿轮和从动齿轮。更少的部件意味着更少的维护,以及更容易和更快的维护。


相反,许多其他计量泵技术包含多达16个活动部件,所有都会磨损。


此外,大多数止回阀由于侵蚀、腐蚀或在阀门球阀和阀座之间夹有外来颗粒而有失效的危险。此外,这些止回阀会造成限制,增加泵所需的净正吸入头(NPSH)。

选择计量齿轮泵的7个技巧

如果你的过程需要一个准确的,可靠的计量齿轮泵,重要的是记住以下提示。


1:正确获取应用数据。

与所有泵的应用一样,必须将正确和完整的应用数据传递给泵制造商。这样做将有助于泵的正确工作和最小的维护。该数据应包括但不限于:

•流量(最小、正常、最大)

•进口和排放压力(最小、正常、最大)

•粘度

•温度(最低、正常、最高)

•处理的流体以及弹性体和金属材料,如果不是普通液体

•是否存在任何固体,如果存在,固体的百分比、固体的最大粒径和固体的硬度

•电机数据(相位,赫兹,电压)和区域分类


2:说明您打算如何使用泵。

在大多数情况下,泵制造商已经看到您的应用程序,或类似的东西,并可能有设计建议,可能证明是更好的选择。


3:不要让泵干了。

大多数齿轮泵需要润滑轴承和密封。根据设计和泵送条件的不同,即使在很短的时间内,这些部件都可能会被损坏。


4:询问你的供应商,他们是否在上游和下游提供必要的或想要的辅助设备,以提高你的泵的性能。

这些部件可能包括过滤器、隔离阀、校准柱和减压阀。

根据泵的需要,泵制造商能够更好地确定过滤器的筛孔尺寸,或者正确地设置减压阀。


5:在从泵排出的管道上安装一个压力安全阀。

大多数容积泵需要在排放管道上安装一个外部压力安全阀。

虽然有些泵可能有一个内部压力安全阀,这通常意味着作为二级预防措施,以保护泵,而不一定是系统管道。

如果管道上可能存在限制,如堵塞的喷嘴、过滤器或隔离阀,大多数当地法规要求在排放管道上安装外部压力安全阀。确保确认此和所有其他适用的规范和要求。


6:如果您打算在使用前或在两次使用之间长时间储存泵,请通知泵制造商。

大多数制造商都有一个长期的储存计划,可能包括在已加工或未喷漆的表面涂上一层油,特殊的包装方法和材料,甚至根据预期的空闲时间的持续时间为电机和泵轴的旋转制定时间表。


7:在安装和启动泵之前,阅读和审查制造商的安装和操作手册。

在这些手册中可以找到有价值的信息,这些信息可以防止灾难性的故障或泵的错误安装。

此外,还有例行维护计划,以保持泵的正常运行,以及故障排除指南,以帮助诊断问题时,它确实发生。


7 Tips for Choosing a Metering Gear Pump

Take advantage of OEM experience to get your system right from the start.

BY ROBERT LIMPER & EMMETT SELLERS COLFAX FLUID HANDLING 


Within the general classification of external gear pumps, precision gear metering pumps are a specialized subset providing accurate, reliable and pulse-free metering performance over a wide range of applications and process fluid conditions.

While many gear pump applications are designed for simple transfer of viscous liquids, others are manufactured with extremely close tolerances, allowing for much higher pressures and the extremely accurate flows required of precision metering type applications.They differ from the pumps used for transfer applications in that internal operating clearances are much tighter, minimizing internal fluid slip and allowing for highly accurate and measured amounts of fluid to be metered and transferred. Due to their extreme close tolerances and smaller gear sizes, these pumps are capable of flows as low as 0.5 cubic centimeters per minute with pressures to 10,000 psi and temperatures from -40 F to 950 F.In the process industries, nothing could be more mission critical than ensuring the integrity of the process itself. The pump systems supporting these processes must be uniquely designed and configured to align with that unique process. Close tolerance precision gear metering pumps in metering applications offer accurate delivery,are reliable in service and have virtually pulse-free fluid delivery performance.

Metering, mixing and spray applications that rely on precision gear metering pumps involve chemicals,extruded plastics, fiber spinning, paints, adhesives and sealants, or other additives supporting either a specific process operation or final product.


In these instances, flow variances due to inconsistent and/or pulsating flow can either completely ruin the end product or produce off-spec product,resulting in productivity losses, increased rework and excessive product waste—all with an end result of increased cost to the manufacturer.


Examples of challenges precision gear metering pumps can tackle include:

• overspraying/overdispensing resulting in excessive material waste and increased manufacturing costs 

• overfeeding additives to account for under-dosing resulting in extra cost and effect on product appeal

• difficulty controlling extruder variations such as pressure fluctuations, viscosity inconsistencies and density changes

• inefficient pressure and volume variations in paint spray equipment applications, affecting quality and productivity on the line

• overfeeding expensive process chemicals to prevent the under-dosing that would affect the finished product quality

• irregular, pulsating delivery of expensive additives


Gear pumps are engineered to provide high wear resistance and dimensional stability, even under extremes of fluid temperatures, pressures, viscosities and abrasive or corrosive composition. Products with viscosities up to 2 million centipoise (cP) can be accommodated. 


Accurate Delivery The volumetric output of a fluid is metered and moved with precision at a constant speed, with minimal pulsations, according to the size of the gear teeth and the speed at which they rotate. Precision metering gear pumps can achieve the tightest pumping clearances,measured in microns, to minimize fluid slip.


Clearances between the gear teeth tips and the side wall can be as low as 0.00015 inches (0.0031 millimeters).These clearances are 20 times thinner than an average sheet of paper.


Manufacturing tolerances on many parts to +/- 50 millionths of an inch with surface finishes as smooth as 4 micro inches or better are possible. A continuous,pulseless stream of dispensing or dosing results as the gear pumps move many small cavities per revolution.


Sustained linear flow can be maintained even during changes in operating speeds, pressures and temperatures.The drive system and incorporation of closed loop speed controller can maintain speed accuracy at 0.1 percent levels.


Reliable in Service Metering gear pumps can be made of many variations of stainless steel for corrosive or sanitary applications,but they are commonly made of hardened tool steel for abrasive applications. Maintenance on a metering gear pump is typically much lower than with other technologies due to the rugged construction and limited number of moving parts. In many cases there are only three moving parts—the drive shaft, the drive gear and the driven gear. Fewer parts means reduced, as well as easier and faster, maintenance.


Conversely, many other metering pump technologies contain as many as 16 moving parts, all subject to wear.


In addition, most have check valves that risk failure due to erosion, corrosion or foreign particles caught between the valve ball and seat. Further, these check valves create restrictions increasing the net positive suction head (NPSH) required for the pump.


Should your process require an accurate, reliable metering gear pump, it is important to keep the following tips in mind.


1:Get the application data right.


As with all pump applications, it is imperative to convey correct and complete application data to the pump manufacturer. Doing so will help the pump work correctly and with minimal maintenance. This data should include but not be limited to:

• flow rate (minimum, normal, maximum)

• inlet and discharge pressures (minimum, normal,maximum)

• viscosity

• temperature (minimum, normal, maximum)

• the fluid being handled as well as elastomer and metal preferences if this is not a common liquid

• whether any solids are present, and if so, the percent of solids, the maximum particle size of solids and the hardness of solids

• motor data (phase, hertz, voltage) and the area classification


2:Convey how you intend to use the pump.


In most cases, the pump manufacturer has seen your application before, or something similar to it, and may have suggestions on designs that may prove to be a better option.


3:Do not let the pump run dry.


Most gear pumps require lubrication to the bearings and seals. Depending on the design and pumping conditions, these parts can be damaged if run dry for even a short period of time.


4:Ask your supplier if they provide ancillary equipment upstream and downstream that will be necessary or desirable to enhance the performance of your pump.


These items may include strainers,isolation valves, calibration columns and pressure relief valves. 


The pump manufacturer is in the better position to identify the mesh size of a strainer, or the proper setting of a pressure relief valve based on the needs of their particular pump.


5:Install a pressure relief valve in the discharge piping from the pump.

Most positive displacement pumps require an external pressure relief valve to be installed in the discharge piping.


Although some pumps may have an internal pressure relief valve, this is typically meant as a secondary precaution to protect the pump, not necessarily the system piping.

Most local codes call for an external pressure relief valve to be installed in the discharge piping if there is the possibility of a restriction in the line such as a plugged nozzle or filter or an isolation valve. Make sure to confirm this and all other applicable codes and requirements.


6:Advise the pump manufacturer if you intend to store the pump for a long period of time before use, or in between uses.


Most manufacturers have a long-term storage plan that may include applying a coat of oil to machined or unpainted surfaces, special packing methods and materials, and even a time schedule for rotation of the motor and pump shaft depending on the anticipated idle time duration.


7:Read and review the manufacturer’s installation and operation manual before you install and start the pump.


There is valuable information to be found in these manuals that may prevent catastrophic failures or incorrect installation of the pump.


There are also routine maintenance schedules to keep your pump up and running as well as a troubleshooting guide to assist in diagnosing a problem when it does occur. 



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