When choosing equipment to remove moisture contained in steam or compressed air, the first things to check are four points: the type of fluid, the bore size and flow rate, the operating pressure and temperature, and the required separation performance. A separator is a device that separates liquid droplets (condensate or moisture) from the fluid in the piping using inertia and centrifugal force, and choosing the wrong one can lead to insufficient separation or excessive pressure loss. To achieve stable product quality and to suppress water hammer and corrosion, selecting a type and size suited to the application and conditions is the starting point.
Key points of this article
- Separators are selected around four axes: fluid type, flow rate, pressure/temperature, and separation performance
- To reliably discharge the separated moisture, combination with downstream trap devices is a prerequisite
- The bore size should be determined from flow rate and pressure loss, not from the piping size
How a separator works and its role
A separator (moisture separator) is a device that removes water droplets mixed into gases such as steam or compressed air. Internal baffle plates or a swirling flow cause an abrupt change in the direction of flow, so that liquid droplets, which have greater inertia than the gas, collide with and adhere to the wall surfaces and are thereby separated. The separated moisture collects at the bottom of the body and is led out of the system through the drain outlet.
The purpose of removing moisture
In steam systems, moisture contained in condensate generated within the piping or in wet steam can cause reduced heat-exchange efficiency, water splashing onto products, and can be a contributing factor to water hammer. Supplying steam with high dryness is important for stabilizing the quality of processes such as heating, drying, and sterilization. In compressed air systems as well, moisture can be a cause of coating defects, air-tool malfunctions, and piping corrosion. The separator serves to remove such moisture in advance.
Combination with trap devices
A separator is a device that “separates” moisture, and to continuously and automatically “discharge” the collected moisture, it is common to combine it with a steam trap (for steam systems) or an automatic drain trap (for air systems) downstream. Even if separation performance is high, if the discharge side becomes stagnant, water accumulates inside the body and separation efficiency may drop. Designing separation and discharge as a set is a point that is easily overlooked during selection.
Criteria to check when selecting
Selecting based on flow rate and bore size
The basic approach is to select the bore size from the actual flow rate and the allowable pressure loss, rather than matching it to the size of the connecting piping. If the bore size is too small for the flow rate, pressure loss becomes large; conversely, if it is too large, the flow velocity drops and separation efficiency may decline. In general, separation performance tends to be achieved when used at flow velocities near the rated value, so grasping not only the maximum flow rate but also the flow rate under normal operation makes selection easier.
Pressure, temperature, and materials
The operating pressure and temperature must be selected within the applicable range of the body. The required pressure and heat resistance and the material (cast iron, cast steel, stainless steel, etc.) differ between high-temperature, high-pressure steam applications and compressed-air applications near ambient temperature. Because the options also change depending on whether there are corrosive or sanitary requirements, we recommend organizing the fluid conditions and then confirming the matching specifications.
Installation orientation and maintainability
For a separator, installation in an orientation where the drain reliably falls to the bottom of the body is a prerequisite for separation and discharge. Installation conditions such as mounting on horizontal piping and the direction of the drain outlet are specified for each type. In addition, securing space that allows for inspection, blowdown, and maintenance of the downstream trap makes long-term operation easier.
Frequently asked questions
Q1. What is the difference between a separator and a steam trap
A1. A separator is a device that separates water droplets from the flowing gas. A steam trap is a device that discharges accumulated condensate, so their roles differ. In many cases, the two are used in combination.
Q2. Is it acceptable for the bore size to be the same as the piping size
A2. It is not necessarily the same. The basic approach is to select it from the flow rate and allowable pressure loss, and it may not match the piping size. Depending on the conditions, a reducer connection is considered.
Q3. Can it also be used with compressed air
A3. It can be used if a type and material suited to air applications are selected. Because the conditions differ from steam applications, please clarify the fluid and confirm the specifications.
Q4. What level of separation performance can be expected
A4. It varies depending on the type and operating conditions. In general, performance tends to be achieved near the rated flow rate. We recommend treating the figures as a guide and confirming them under actual conditions.
Q5. Is there a specified orientation for installation
A5. In many types, an orientation in which the drain collects at the bottom is a prerequisite. Please install according to the installation conditions in the instruction manual or specifications.
Q6. When replacing existing equipment, is the same bore size acceptable
A6. If the operating conditions have not changed, replacement with an equivalent product is the basic approach. If the flow rate or pressure has changed, it is safer to reselect from the conditions anew.
Summary
Selecting a separator basically comes down to organizing the four points of fluid type, flow rate, pressure/temperature, and separation performance, and considering separation and discharge as a set. By determining the bore size from the flow rate rather than the piping size, and by choosing specifications that match the conditions, including installation orientation and maintainability, you are more likely to achieve quality stabilization and equipment protection through moisture removal.
If you have concerns such as “I know the piping size but am not confident about selecting the bore size from the flow rate,” “I know the maximum flow rate but the flow rate under normal operation is unknown,” “I want to select an equivalent to an existing separator but cannot read the specifications,” or “I would like to consult about how to combine it with a downstream trap,” please organize your operating conditions and send your technical or selection inquiry to Yoshitake. We will propose a selection suited to your operating environment.