A brass aspirator. The water inlet and outlet are at the top and bottom, respectively; the air inlet is on the side.
Other namesEductor-jet pump,A vacuum ejector, or simply ejector, is a type of vacuum pump, which produces vacuum by means of the Venturi effect.
In an ejector, a working fluid (liquid or gaseous) flows through a jet nozzle into a tube that first narrows and then expands in cross-sectional area. The fluid leaving the jet is flowing at a high velocity which due to Bernoulli's principle results in it having low pressure, thus generating a vacuum. The outer tube then narrows into a mixing section where the high velocity working fluid mixes with the fluid that is drawn in by the vacuum, imparting enough velocity for it to be ejected, the tube then typically expands in order to decrease the velocity of the ejected stream, allowing the pressure to smoothly increase to the external pressure.
The strength of the vacuum produced depends on the velocity and shape of the fluid jet and the shape of the constriction and mixing sections, but if a liquid is used as the working fluid, the strength of the vacuum produced is limited by the vapor pressure of the liquid (for water, 3.2 kPa or 0.46 psi or 32 mbar at 25 °C or 77 °F). If a gas is used, however, this restriction does not exist.
If not considering the source of the working fluid, vacuum ejectors can be significantly more compact than a self-powered vacuum pump of the same capacity.
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The cheap and simple water aspirator is commonly used in chemistry and biology laboratories and consists of a tee fitting attached to a tap and has a hose barb at one side. The flow of water passes through the straight portion of the tee, which has a restriction at the intersection, where the hose barb is attached. The vacuum hose should be connected to this barb. In the past, water aspirators were common for low-strength vacuums in chemistry benchwork. However, they are water-intensive, and depending on what the vacuum is being used for (e.g. solvent removal), they can violate environmental protection laws such as the RCRA by mixing potentially hazardous chemicals into the water stream, then flushing them down a drain that often leads directly to the municipal sewer. Their use has decreased somewhat as small electric vacuum pumps are far more effective, environmentally safe, and have become more affordable, but the unmatched simplicity and reliability of this device have caused it to remain popular for small labs or as a backup.
Another, much larger version of this device is used in maritime operations as a device to dewater (drain) areas in a ship that have been flooded in emergency situations. Typically referred to as an eductor in these applications, this is preferred over electrical pumps due to their simplicity, compact size, and greatly mitigated risk of explosion in the event that flammable liquids and/or vapors are present. Additionally, unlike many mechanical pumps, they can also pass debris as the eductor has no moving parts that can be fouled. This makes an eductor especially useful in situations where fitting a debris strainer to the suction port will present more issues than it resolves. The size of the debris that can be passed depends on the physical size of the eductor. Sizes, flow ratings, and applications vary, including eductors that are permanently installed (typically used in very large spaces, such as a ship's main engine room), or portable models that can be lowered into spaces by a rope and supplied and drained through firefighting hoses. Most are supplied through a ship's firefighting main, and portable models can also be supplied by an emergency pump, provided it can supply sufficient flow to operate the eductor.
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The industrial steam ejector (also called the "steam jet ejector", "steam aspirator", or "evactor") uses steam as a working fluid and multistage systems can produce very high vacuums. Due to the lack of delicate moving parts and the flow of steam providing somewhat of cleaning action, steam ejectors can handle gas flows containing liquids, dust, or even solid particles that would damage or clog many other vacuum pumps. Ejectors made entirely from specialised materials such as PTFE or graphite have allowed usage of extremely corrosive gasses, since steam ejectors have no moving parts they can be constructed in their entirety from almost any material that has sufficient durability.
In order to avoid using too much steam or impractical operating pressures, a single steam-ejector stage is generally not used to generate vacuum below approximately 10 kPa (75 mmHg).[1] To generate higher vacuum, multiple stages are used; in a two-stage steam ejector, for example, the second stage provides vacuum for the waste steam output by the first stage. Condensers are typically used between stages to significantly reduce the load on the later stages. Steam ejectors with two, three, four, five and six stages may be used to produce vacuums down to 2.5 kPa, 300 Pa, 40 Pa, 4 Pa, and 0.4 Pa, respectively.[1]
Steam ejectors are also suitable for pumping many liquids since if the steam can be easily condensed into the liquid then there is no need to separate the working fluid or manage a mist of liquid droplets. This is the manner in which a steam injector operates.
An additional use for the injector technology is in vacuum ejectors in continuous train braking systems, which were made compulsory in the UK by the Regulation of Railways Act . A vacuum ejector uses steam pressure to draw air out of the vacuum pipe and reservoirs of continuous train brake. Steam locomotives, with a ready source of steam, found ejector technology ideal with its rugged simplicity and lack of moving parts. A steam locomotive usually has two ejectors: a large ejector for releasing the brakes when stationary and a small ejector for maintaining the vacuum against leaks. The exhaust from the ejectors is invariably directed to the smokebox, by which means it assists the blower in draughting the fire. The small ejector is sometimes replaced by a reciprocating pump driven from the crosshead because this is more economical of steam and is only required to operate when the train is moving.
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Commonly called an air ejector, Venturi pump, or vacuum ejector. This ejector is similar in operation to the steam ejector but uses high-pressure air as the working fluid. Multistage air ejectors can be used, but since air cannot easily be condensed at room temperature, an air ejector is usually limited to two stages as each subsequent stage would have to be significantly larger than the last. These are commonly used in pneumatic handling equipment when a small vacuum is required to pick up objects since compressed air is often already present to power other parts of the equipment. Air ejectors used to suction liquids directly will produce a fine mist of droplets, this is how airbrushes and many other spraying systems operate, but when a spray is not required it is typically an undesirable effect that limits the applications to gas suction.
The basic elements of an ejector[
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High Vacuum Pumping Equipment, B. D. Power, New York: Reinhold Publishing Corporation, , chapter 4.
Why You May Need One
A sewage ejector pump, or pump-up ejector system, pumps sewage water uphill from a bathroom, laundry room, or other plumbing fixture below the level of the main sewer or septic line.
Typically, sewage and drain wastewater is moved downward by gravity to the main sewer or septic line. So, if the waste needs to move upward, a sewage ejector pump is required.
Learn about sewage ejector pumps and determine if you need one for your home.
A sewage ejector pump lifts waste or sewage water upward to the main sewer or septic line. It operates much like a groundwater sump pump, but instead of moving clean water, it pumps sewage and waste.
Why You May Need a Sewage Ejector Pump
You may need to install a sewage ejector pump if your home has a basement or below-grade (that is, below ground level) bathroom or laundry room. If the sewer line runs upward, a pump is needed. If the line runs downward, a pump is not needed.
Sewage ejector pumps are also common in homes with septic drain-field systems. Homes in rural locations may have a septic drainage field or holding tank above the bathroom or laundry room.
How Sewage Ejector Pumps Work
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Sewage ejector pumps rest in a below-grade sump basin that holds about 30 gallons of waste. The process starts when wastewater is expelled from a toilet or laundry room:
Pros and Cons
Pros
Cons
Cost
Installing a sewage ejector pump in a home typically costs $2,325, with an average cost range of $850 to $3,800.
Sewage ejector pumps are available at local home improvement stores, online, and through your local plumbing supply house. They are also available for commercial applications, but these require a much larger sump basin.
Low $850 Average $2,325 High $3,800Maintenance and Repair
It's usually best to have a professional maintain and repair your sewage ejector pump. But there are a few basic maintenance duties you can take on yourself.
Frequently check the oil level and top it off as needed. Make sure that the pump is working by turning the circuit breaker off and on again. With the pump turned off at the circuit breaker, wipe down the pump's casing with a clean, dry cloth.
System Requirements
A vent is required for a sewage ejector pump installation to equalize pressure during pumping and to provide an outlet for sewer gasses. The vent comes out of the sump pit and is either connected to an existing vent (soil) stack or runs up and through the roof.
The outlet pipe leaving the sewage ejector pump is usually 2 to 4 inches in diameter, connecting to the 3- to 6-inch main sewer line. Between the pump outlet point and the junction with the main sewer line, there is always a check valve to make sure that nothing drains back into the sump basin after the wastewater is pumped out. When it is installed properly, the top of the sump basin is sealed so that no waste or smell can come out of the top of the basin.
Installation Considerations
Before installing a sewage ejector pump, check with your local building department. Different communities may have unique plumbing and building codes and permit requirements. Any work involving septic or sewer lines will likely require a permit.
Ejector pumps come in various sizes (horsepower), and the basins have different hold capacities. For the average residential installation, a standard pump kit with a 1/2 to 3/4 horsepower motor and 30- or 40-gallon is usually sufficient.
FAQ
What happens if an ejector pump fails?
If an ejector pump fails, raw sewage can back up into your house. If the pump fails, stop using all plumbing in the house and immediately call a plumber.
How do I know if my ejector pump is working?
You can see if your ejector pump is working by pouring two to three gallons of clean water into an empty ejector basin. If the pump turns on and pumps out water, it is working properly.
How far can an ejector pump push sewage?
An ejector pump typically can push sewage up to 30 feet vertically (or, head height). Gravity takes over after the waste reaches the head height.
8 Essential Tasks to Do Regularly for Septic Tank Maintenance
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How Much Does an Ejector Pump Cost? HomeAdvisor.
Complete Guide to Sewage Grinder Pumps. Zoeller Pump Company.
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