Diaphragm pump

A diaphragm pump (also known as a Membrane pump) is a positive displacement pump that uses a combination of the reciprocating action of a rubber, thermoplastic or teflon diaphragm and suitable valves on either side of the diaphragm (check valve, butterfly valves, flap valves, or any other form of shut-off valves) to pump a fluid.

There are three main types of diaphragm pumps:

Those in which the diaphragm is sealed with one side in the fluid to be pumped, and the other in air or hydraulic fluid. The diaphragm is flexed, causing the volume of the pump chamber to increase and decrease. A pair of non-return check valves prevent reverse flow of the fluid.[1]

Those employing volumetric positive displacement where the prime mover of the diaphragm is electro-mechanical, working through a crank or geared motor drive, or purely mechanical, such as with a lever or handle. This method flexes the diaphragm through simple mechanical action, and one side of the diaphragm is open to air.[2]

Those employing one or more unsealed diaphragms with the fluid to be pumped on both sides. The diaphragm(s) again are flexed, causing the volume to change.

When the volume of a chamber of either type of pump is increased (the diaphragm moving up), the pressure decreases, and fluid is drawn into the chamber. When the chamber pressure later increases from decreased volume (the diaphragm moving down), the fluid previously drawn in is forced out.[3] Finally, the diaphragm moving up once again draws fluid into the chamber, completing the cycle. This action is similar to that of the cylinder in an internal combustion engine. Diaphragm Pumps deliver a hermetic seal between the drive mechanism and the compression chamber, allowing the pump to transfer, compress, and evacuate the medium without a lubricant.[4]

An elastomeric diaphragm can be used as a versatile dynamic seal that removes many of the limitations found with other sealing methods. They do not leak, offer little friction, and can be constructed for low pressure sensitivity. With the right material consideration, diaphragms can seal over a wide range of pressures and temperatures without needing lubrication or maintenance.

A bicycle pump is a type of positive-displacement pump specifically designed for inflating bicycle tires. It has a connection or adapter for use with one or both of the two most common types of valves used on bicycles, Schrader or Presta. A third type of valve called the Dunlop (or Woods) valve exists, but tubes with these valves can be filled using a Presta pump.[1]

Several basic types are available:

Floor pumps

Frame mounted

Compact or mini

Foot operated

Double action

In its most basic form, a bicycle pump functions via a hand-operated piston. During the up-stroke, this piston draws air through a one-way valve into the pump from the outside. During the down-stroke, the piston then displaces the air from the pump into the bicycle tire. Most floor pumps, also commonly called track pumps, have a built in pressure gauge to indicate tire pressure.

Electrically-operated pumps intended to inflate car tires (as available in most service stations) can in principle be used to inflate a bicycle tire if the right type of connection is available. Some such pumps are designed to cut off before a suitable pressure (much higher for a bicycle than a car tire), and will much underinflate the tire. Others may not cut off, but deliver a high rate of flow to fill the larger car tire, with a risk of overinflating and bursting a bicycle tire unless it is stopped with split-second timing.

History

No day has been established as to when the first bicycle pump was invented, but it is believed to have been in or around 1887, which is when the first inflatable tire or pneumatic tire was produced by John Boyd Dunlop of Scotland. The first bicycle pump consisted of a metal cylinder that had a metal rod running down the middle of it. This would have forced the air out of the cylinder and then sucked in new air when the metal rod was pulled up again. Many modern pumps use a very similar method, while some, such as the electric pumps, use an automated pumping mechanism.

How they work

The bicycle pump compresses air. When the cylinder is compressed, air is pushed down the tube of the pump and then into the tire via the valve, which is forced open by the pressure of the air. When the handle is pulled up again, the valve shuts off automatically so that the air cannot escape from the tire, and new air is forced back into the cylinder so the process can be repeated. Some pumps have a gauge that shows the pressure of air that is forced into the tire. Once the tire is at the correct pressure, the pump valve can be removed from the tire, and the cap can be replaced on the tire valve.

There are two main types of tire valves to which the bicycle tire pump attaches. These are the Presta valve and the Schrader valve. Some pumps fit both types of valves, whereas others do not, but adapters are available that enable the pump to fit any type of valve. "All valves adjustable connecting systems," also known as AVACS, enable the pump to fit any type of valve found on a bicycle, and it also has the capacity to fit onto other universal inflatable products, such as balls, paddling pools, and rubber rings. The AVACS feature is commonly available on pump models and can also be bought as a separate valve attachment.

Types

There are three main types of bicycle pumps

Stand pump

Hand pump

Foot pump

Stand pump

Also known as a floor or track pump. To operate, the user rests the base of the pump on the floor, resting feet at the base, and pulls and pushes full strokes with handles. An additional tube must connect the pump to the fill valve, which may create dead volume.

Hand pump

There are two basic types: tubed and integral. The tubed type requires a separate tube to connect the pump to the valve. These have the advantage that they are cheap, but are inefficient compared to other pumps. They also have a lot of joints from which air can escape.

Integral pumps have a hole in the side with a rubber washer that fits round the valve. This is frequently compressed on to the valve by an extra lever. Because it is well sealed, rigid and has little dead volume, this type of pump is very efficient. An 8" integral will typically pump faster than an 18" tubed. These type of pumps will run the risk of shredding the tube valves, especially on those with presta valves.

A simple pump has a cupped fiber or plastic piston. On the forward stroke the air pushes the sides of the cup against the cylinder, so forming a seal; it provides its own valve. Then this piston can push the air out of the hole at the far end.

Some of the most efficient pumps are double action pumps. By sealing the piston in the cylinder at both ends they can force air into the tire on both strokes.

Pumps can be fitted to a bracket on the bike frame, either a clamp on, screw on, or a braze-on peg, or they can be carried in a pannier or other bag on the bike, or they can be carried by the rider in a backpack, pocket, etc. Pumps carried on the bike are often fairly small to reduce weight. Because of their size, the volume of air that these pumps can provide is somewhat limited compared to a floor pump, so quite a lot of pumping may be needed.

Foot pumps

These pumps are often not specifically designed for bicycle use. They do not generate very high pressures so do not work well for narrow road-bike tires, but are fine for large low-pressure tires as found on mountain bikes.

Because they are designed for cars they fit schrader valves. If the bicycle has presta valves a small brass reducer is required in order to use the pump.

CO2 inflators

Gas-filled cylinders for bicycles have an unclear history but appear to have appeared between the two World Wars. One story says they were made "by a rider after watching a café proprietor charge up the glass of beer he had ordered from a bottle of carbon dioxide."[2]

The pumps generally used liquefied gas that could not be replaced at home. A later version, which had more success, used a cartridge sold originally for drinks siphons. A lever broke the cartridge and enough gas escaped to inflate a tire.

Modern gas pumps are often used by mountain bike or road bike racers who need to save weight, and to save time if they puncture during a race. They can be a one-time pump or a pump that can be fitted with a replacement cartridge. Most pumps use carbon dioxide and standard-threaded 16g CO2 canisters. Carbon dioxide leaks out of a rubber inner tube more rapidly than air -

despite its larger size, the CO2 molecule is slightly soluble in rubber and a tire may go flat within a few days.

Electric pump

12 volt air compressors made for automobile tires are also compatible with bicycle tires. A portable jump-starter for automobiles can sometimes be used to power these types of pumps. Even non-standard DIY 12 volt electric systems that are primarily for bicycle lighting are sometimes used to power these pumps when cigar lighter receptacles are installed. A main advantage to electric pumps is that recent ones take up less space than hand or foot pumps which makes them suitable for well-equipped bicycles with DIY 12 volt electric systems to use when basket space is of the essence.

Tire pressure

The pressure rating of tires is usually stamped somewhere on the sidewall. This may be in psi (pounds per square inch) or bar. The pressure rating could be indicated as "Maximum Pressure," or "Inflate to and will usually give a range (for example, 90-120 psi, or 35-60 psi). Inflating to the lower number in the pressure range will increase traction and make the ride more comfortable. Inflating to the higher number will make the ride more efficient and will decrease the chances of getting a flat tire but a firmer ride must be expected.

Pressure output

The maximum pressure, or how much air the pump can force into a tire, is an important consideration. The pump needs to match or exceed the stated air pressure the tires can handle. If the maximum air pressure is too low, it will not be able to adequately inflate the tires, no matter how hard it is used.

Air compressor

An air compressor is a device that converts power (using an electric motor, diesel or gasoline engine, etc.) into potential energy stored in pressurized air (i.e., compressed air). By one of several methods, an air compressor forces more and more air into a storage tank, increasing the pressure. When tank pressure reaches its upper limit the air compressor shuts off. The compressed air, then, is held in the tank until called into use. The energy contained in the compressed air can be used for a variety of applications, utilizing the kinetic energy of the air as it is released and the tank depressurizes. When tank pressure reaches its lower limit, the air compressor turns on again and re-pressurizes the tank.

Classification

According to the pressure delivered

Low-pressure air compressors (LPACs), which have a discharge pressure of 150 psi or less

Medium-pressure compressors, which have a discharge pressure of 151 psi to 1,000 psi

High-pressure air compressors (HPACs), which have a discharge pressure above 1,000 psi

According to the design and principle of operation

Rotary screw compressor

Turbo compressor

Displacement type

There are numerous methods of air compression, divided into either positive-displacement or negative-displacement types.

Positive displacement

Positive-displacement compressors work by forcing air into a chamber whose volume is decreased to compress the air. Common types of positive displacement compressors are:-

Piston-type: air compressors use this principle by pumping air into an air chamber through the use of the constant motion of pistons. They use one-way valves to guide air into a cylinder chamber, where the air is compressed.[1]

Rotary screw compressors: use positive-displacement compression by matching two helical screws that, when turned, guide air into a chamber, whose volume is decreased as the screws turn.

Vane compressors: use a slotted rotor with varied blade placement to guide air into a chamber and compress the volume. A type of compressor that delivers a fixed volume of air at high pressures.

Negative displacement

Negative-displacement air compressors include centrifugal compressors. In this type, a rotating component imparts its kinetic energy to the air which is eventually converted into pressure energy. These use centrifugal force generated by a spinning impeller to accelerate and then decelerate captured air, which pressurizes it. [1]

Cooling

Due to adiabatic heating, air compressors require some method of disposing of waste heat. Generally this is some form of air- or water-cooling, although some (particularly rotary type) compressors may be cooled by oil (that is then in turn air- or water-cooled)[3] and the atmospheric changes also considered during cooling of compressors.

Applications

Portable air compressor for powering tools, such as jackhammers

Air compressors have many uses, including: supplying high-pressure clean air to fill gas cylinders, supplying moderate-pressure clean air to a submerged surface supplied diver, supplying moderate-pressure clean air for driving some office and school building pneumatic HVAC control system valves, supplying a large amount of moderate-pressure air to power pneumatic tools, such as jackhammers, for filling tires, and to produce large volumes of moderate-pressure air for large-scale industrial processes (such as oxidation for petroleum coking or cement plant bag house purge systems).

Most air compressors either are reciprocating piston type, rotary vane or rotary screw. Centrifugal compressors are common in very large applications. There are two main types of air compressor's pumps: oil-lubed and oil-less. The oil-less system has more technical development, but is more expensive, louder and lasts for less time than oil-lubed pumps. The oil-less system also delivers air of better quality.

The most common types of air compressors are: electric or gas/diesel powered compressors. The power of a compressor is measured in HP (Horsepower) and CFM (cubic feet of air per minute). The gallon size of the tank tells you how much compressed air "in reserve" is available. Gas/diesel powered compressors are widely used in remote areas with problematic access to electricity. They are noisy and require ventilation for exhaust gases. Electric powered compressors are widely used in production, workshops and garages with permanent access to electricity. Common workshop/garage compressors are 110-120 Volt or 230-240 Volt. Compressor tank shapes are: "pancake", "twin tank", "horizontal", and "vertical". Depending on a size and purpose compressors can be stationary or portable.

Air compressor types

While there are compressors that use rotating impellers to generate air pressure, positive-displacement compressors are more common and include the models used by homeowners, woodworkers, mechanics and contractors. Here, air pressure is increased by reducing the size of the space that contains the air. Most of the compressors you'll run across do this job with a reciprocating piston.

Like a small internal combustion engine, a conventional piston compressor has a crankshaft, a connecting rod and piston, a cylinder and a valve head. The crankshaft is driven by either an electric motor or a gas engine. While there are small models that are comprised of just the pump and motor, most compressors have an air tank to hold a quantity of air within a preset pressure range. The compressed air in the tank drives the air tools, and the motor cycles on and off to automatically maintain pressure in the tank.

At the top of the cylinder, you'll find a valve head that holds the inlet and discharge valves. Both are simply thin metal flaps–one mounted underneath and one mounted on top of the valve plate. As the piston moves down, a vacuum is created above it. This allows outside air at atmospheric pressure to push open the inlet valve and fill the area above the piston. As the piston moves up, the air above it compresses, holds the inlet valve shut and pushes the discharge valve open. The air moves from the discharge port to the tank. With each stroke, more air enters the tank and the pressure rises.

Typical compressors come in 1- or 2-cylinder versions to suit the requirements of the tools they power. On the homeowner/contractor level, most of the 2-cylinder models operate just like single-cylinder versions, except that there are two strokes per revolution instead of one. Some commercial 2-cylinder compressors are 2-stage compressors–one piston pumps air into a second cylinder that further increases pressure.

Compressors use a pressure switch to stop the motor when tank pressure reaches a preset limit–about 125 psi for many single-stage models. Most of the time, though, you don't need that much pressure. Therefore, the air line will include a regulator that you set to match the pressure requirements of the tool you're using. A gauge before the regulator monitors tank pressure and a

gauge after the regulator monitors air-line pressure. In addition, the tank has a safety valve that opens if the pressure switch malfunctions. The pressure switch may also incorporate an unloader valve that reduces tank pressure when the compressor is turned off.

Many articulated-piston compressors are oil lubricated. That is, they have an oil bath that splash-lubricates the bearings and cylinder walls as the crank rotates. The pistons have rings that help keep the compressed air on top of the piston and keep the lubricating oil away from the air. Rings, though, are not completely effective, so some oil will enter the compressed air in aerosol form.

Having oil in the air isn't necessarily a problem. Many air tools require oiling, and inline oilers are often added to increase a uniform supply to the tool. On the down side, these models require regular oil checks, periodic oil changes and they must be operated on a level surface. Most of all, there are some tools and situations that require oilfree air. Spray painting with oil in the airstream will cause finish problems. And many new woodworking air tools such as nailers and sanders are designed to be oilfree so there's no chance of fouling wood surfaces with oil. While solutions to the airborne oil problem include using an oil separator or filter in the air line, a better idea is to use an oilfree compressor that uses permanently lubricated bearings in place of the oil bath.

A variation on the automotive-type piston compressor is a model that uses a one-piece piston/connecting rod. Because there is no wrist pin, the piston leans from side to side as the eccentric journal on the shaft moves it up and down. A seal around the piston maintains contact with the cylinder walls and prevents air leakage.

Where air requirements are modest, a diaphragm compressor can be effective. In this design, a membrane between the piston and the compression chamber seals off the air and prevents leakage.

Compressor power

One of the factors used to designate compressor power is motor horsepower. However, this isn't the best indicator. You really need to know the amount of air the compressor can deliver at a specific pressure.

The rate at which a compressor can deliver a volume of air is noted in cubic feet per minute (cfm). Because atmospheric pressure plays a role in how fast air moves into the cylinder, cfm will vary with atmospheric pressure. It also varies with the temperature and humidity of the air. To set an even playing field, makers calculate standard cubic feet per minute (scfm) as cfm at sea level with 68 degrees F air at 36% relative humidity. Scfm ratings are given at a specific pressure–3.0 scfm at 90 psi, for example. If you reduce pressure, scfm goes up, and vice versa.

You also may run across a rating called displacement cfm. This figure is the product of cylinder displacement and motor rpm. In comparison with scfm, it provides an index of compressor pump efficiency.

The cfm and psi ratings are important because they indicate the tools that a particular compressor can drive. When choosing a compressor, make sure it can supply the amount of air and the pressure that your tools need.

How Air Compressors Work

It’s easy to think of air compressors as a tool that is very common however, things were not like that in the past. In fact not that long ago a compressor isn’t something you would have found in a workshop or factory.

Instead, tools used in the shop were powered by a centralized source which transferred the power in various ways depending on the tool. Usually it was through a system of wheels, belts or drive shafts. It was a large mechanical system that was way too bulky and way too expensive, and therefore only available to professionals.Nowadays we come across air compressors pretty much everywhere. They’re common place in gas stations where we generally use them to inflate tires. They can be found in factories, workshops, even your local mechanic will make use of a tool like this.

Power tools such as sanders, grinders, staplers, nail guns, spray guns, drills, impact wrenches, and plenty of others are powered by them as well. You can also buy one for yourself online, at your local hardware store, or home depot.

Of course, the biggest advantage of compressors over a centralized power source is their small size, and the fact they don’t require a massive motor. They are also quieter, more durable, and some of them are highly portable. But, I am getting way ahead of myself because you’re here to find out how air compressors work. So, here we go!

Basic Piston Functionality

Air compressors function based on a very simple principle. When the air is compressed, its volume decreases whereas the pressure increases.

The most common way to achieve this is with the help of a reciprocating piston. There are compressors which employ rotating impellers for the purpose of creating air pressure, but I will discuss the different types in a separate article. Those which are built around a reciprocating piston are more common, and if you’re familiar with how internal combustion engines work, you will know piston compressors function in a similar manner.

Each reciprocating piston compressor has a crankshaft, connecting rod, a piston, cylinder, and a valve head. In order for the entire mechanism to work, you need power. Air compressors are usually powered by electricity or gas depending on the model. Most compressors also have a tank which is there to store compressed air for the purpose of keeping the air pressure within a set range while powering various air tools. But, let’s get back to the mechanics of it (I used an image of a liquid reciprocating piston pump to explain this (source: NVC), but with air this works basically the same)

At the top of every compressor cylinder there is a valve head that contains both the inlet and discharge valve which are basically metal flaps. These open and close and are located on top of the valve plate. When the piston moves down inside the cylinder in the space above the piston a vacuum is created.

Now, here’s the clever bit. The difference in pressure on the inside of the cylinder to the outside allows the atmospheric pressure to open the inlet valve. The air then enters the area where the

vacuum used to be, and is compressed by the piston which is now going up. The inlet valve closes and the discharge valve is opened. The compressed air is stored inside the tank thereby increasing the pressure.

Dual Piston

There are variations to this approach but the basic principle is the same. Dual-piston compressors are also very common, and they function in the same way as their single-piston counterparts do. The only real difference is there are two strokes per revolution and not one. The most common variation of a dual-piston compressor is the two-stage compressor which uses one piston to pump air into a second cylinder which creates greater pressure.

In order to keep the pressure within the desired limits, and to prevent the tank from exploding each air compressor has a switch which cuts the power to the motor when pressure inside the tank has reached the limit (which is usually around 125 PSI). In order to calibrate the pressure depending on the power tool connected to the compressor there is a regulator as well as gauges before and after the regulator.

These measure the pressure inside the tank and air-line respectively. In case the pressure switch doesn’t go off, there is a safety valve as well as an unloader valve which is there to reduce pressure inside the tank when the compressor is not being used.

Lubrication

Another major thing you should know about air compressors is the way they are lubricated. You will come across terms like “oil-free pump”, or “oil-lubricated”. Oil-lubricated pumps have an oil bath which lubricates the bearing and walls on the inside of the cylinder. The air and oil are kept separate with the help of the piston rings, but they are not fool-proof so there will be some mixing of air and oil which can be problematic.

On one hand, power tools need to be lubricated anyways so there is no harm in having some of the oil enter the air stream, but if you’re using air tools in woodworking or painting you will mess up the finish. Oil-free pumps have permanently lubricated bearings instead of an oil bath, and they don’t require the same kind of maintenance as oil-lubricated pumps do.