The profile of a splined shaft or hub is designated by stating, in the following order:

The number of splines N

The minor diameter d

The outside diameter D.

For example, shaft (or hub) 6 × 23 × 26.

Tolerances on holes and shafts

Tolerances on hole						Tolerances on shaft			Mounting type
Not treated after broaching			Treated after broaching
B	D	d	B	D	d	B	D	d
H9	H10	H7	H11	H10	H7	d10	a11	f7	Sliding
						f9	a11	g7	Close sliding
						h10	a11	h7	Fixed

Numbers 0–6 Morse tapers and 5% metric tapers

Numbers 1-6 Morse tapers and Nos 1-3 Brown & Sharpe tapers

Designation and dimensions

Thread specification

Noses Nos 65–80

Note:– For spindle nose No. 60, the tenons can be fixed by two screws, as for the spindle noses Nos 65–80

Noses Nos 65–80

Complementary dimensions

Thread specification

Designation and dimensions

These can deliver compressed air to suit the requirements of any system. They can also deliver air at higher pressures than vane and screw compressors. On the downside, they are noisier than vane and screw compressors and their output pulsates and requires to be fed into a receiver to smooth out the flow. Single cylinder compressors are the worst in this respect. Multistage piston compressors are more efficient due mainly to intercooling between the stages. They are capable of higher maximum pressures.

Diaphragm compressors

These are small scale inexpensive reciprocating type compressors of limited output capable of delivering oil-free air for very small systems. Since the air is free from oil they are widely used for small scale spray painting and air-brush applications. They are usually used for portable, stand-alone compressors, by contractors on site for powering such devices as staple guns.

Rotary vane compressors

These are quiet, inexpensive and deliver a steady stream of compressed air without pulsations associated with the piston and diaphragm types. Lubrication of the vane edges is required by a recirculating lubrication system, with the oil being purged from the air before delivery. Multistage vane compressors are available with intercooling between the stages where higher pressures and larger volumes of air are required. The principle operation is shown in following figure.

Screw compressors

These are quiet, efficient but expensive and are usually chosen to supply large scale factory installations The principle of operation is shown in figure ‘the screw compressor’. It can be seen that a rotor with male lobes meshes with a smaller diameter rotor with female lobes. Oil not only lubricates the bearings but also seals the clearances between the rotors and cools the air before purged from the air at the point of discharge. The figure ‘compressor types: typical scope’ shows the scope of the main types of compressor described above.

These are the simplest and most robust positive displacement pump, having just two moving parts as shown in figure ‘gear pump’. Only one gear needs to be driven by the power source. The direction of rotation of the gears should be noted since they form a partial vacuum as they come out of mesh, drawing fluid into the inlet chamber. The oil is carried round between the gear teeth and the outer casing of the pump resulting in a continuous supply of oil into the delivery chamber. The pump displacement, the volume of fluid delivered, is determined by the volume of fluid between each pair of teeth and the speed of rotation. The pump delivers a fixed volume of fluid for each rotation and the outlet port pressure is determined by the ‘back-pressure’ opposing the flow in the rest of the system. This type of pump is used up to pressures of about 150 bar and about 6750 l/min. At 90% the volumetric efficiency is the lowest of the pump types to be described in the section. There are a number of variations on the gear pump available including the internal gear pump and the lobe pump. A lobe pump is shown in figure ‘the lobe pump’.

Vane pumps

The relatively low volumetric efficiency of the gear type pump stems from clearances between the teeth, and between the gears and the outer casing. These sources of leakage are largely over come in vane type pumps by the use of spring loaded vanes as shown in figure ‘unbalanced vane pump’. Vane type hydraulic pumps are similar in principle to the vane type compressor described in Section 5.6.3 except that when delivering oil they are self-lubricating. An alternative design is shown in figure ‘balanced vane pump’.

Piston pumps

Reciprocating force pumps are only used on very large scale applications in conjunction with an accumulator to smooth out the pulsations. Nowadays, for most applications requiring multiple piston pumps, the pistons and cylinders are arranged radially as shown in figure ‘radial piston pump’. The pump consists of several hollow pistons inside a stationary cylinder block. Each piston has spring loaded inlet and outlet valves. As the cam rotates, fluid is transferred relatively smoothly from the inlet port to the outlet port. The pump shown in figure ‘piston pump with stationary can and rotating block’ is similar in principle but uses a stationary cam and a rotating cylinder block. This arrangement removes the need for multiple inlet and outlet valves and is consequently more simple, reliable and cheaper to manufacture and maintain, hence this is the more commonly used type.

Axial (swash plate) pumps

This is also a multiple piston pump. The pistons are arranged in a rotating cylinder block so that they are parallel to the axis of the drive shaft as shown in following figure. The piston stroke is controlled by an angled swash plate as shown. Each piston is kept in contact with the swash plate by spring pressure or by a rotating shoe plate linked to the swash plate. Pump capacity is controlled by altering the angle of the swash plate. The larger the angle the greater the rate of flow for a given speed of rotation. The maximum swash plate angle is limited by the maximum designed piston stroke length. Zero flow rate is achieved when the swash plate is perpendicular to the drive shaft. Reversing the swash plate angle reverses the direction of fluid flow through the pump.

All types of piston pumps have very high volumetric efficiency and can be used at the highest hydraulic pressures. They are more complex than vane and gear pumps and are, therefore more expensive in first cost and to maintain. The following table compares the advantages and limitations of various types of hydraulic pumps.

Comparison of hydraulic pump types

Pneumatic

For general applications these can be the radial piston and cylinder type as shown in figure ‘the piston motor’ where high power at moderate speeds is required. They are bulky, costly and noisy and require a silencer fitted to the exhaust system. A cheaper and lighter solution where lower power and higher speeds are required is the vane motor as shown in figure ‘the vane motor’. For applications, such as small portable drills, die-grinders and dental type drills for fine instrument work air turbines are available.

Hydraulic

Gear motors and vane motors are the most widely used. These are similar to the gear and vane type pumps described earlier. The direction of rotation depends on the direction of fluid flow.

Hydraulic and pneumatic symbols.

Symbol	Description
	Source of energy – Hydraulic
	Source of energy – Pneumatic
	Hydraulic pump Fixed displacement One flow directions
	Hydraulic pump Variable displacement One flow directions
	Hydraulic motor Fixed displacement One flow directions
	Hydraulic motor Variable displacement Two flow directions of rotation
	Air compressor
	Pneumatic motor Fixed displacement One flow directions
	Accumulator – Gas losded
	Air receiver
	Directional control 2/2 valve
	Directional control 3/2 valve
	Directional control 4/2 valve
	Directional control 4/3 valve
	Directional control 5/2 valve
	Directional control 3/3 valve – Closed centre – Spring-centred, pilot operated
	Pressure relief valve – Single stage – Adjustable pressure
	Pressure reducing Valve – With relief – Pneumatic
	Non-return valve
	One-way restrictor or flow control valve
	Hydraulic cvlinder – Double-acting
	Pneumatic cylinder – Double-acting
	Cylinder –Double-acting –Double-ended Piston rod Hydraulic
	Pneumatic cylinder – Single-acting – Spring return
	Cylinder – Double-acting – Adjustable cushions both ends Pneumatic
	Pressure intensifier – Single fluid – Hydraulic
	Semi-rotary actuator – Double-acting – Hydraulic
	Semi-rotary actuator – Single-acting – Spring return –Pneumatic
	Telescopic cylinder – Double-acting Hydraulic
	Electric motor (from IEC 617)
	Valve control mechanism – By pressure
	Valve control Mechanism – By push button
	–By roller
	–By solenoid – Direct
	– By solenoid – With pressure pilot – Pneumatic
	Ouick-release coupling – With non-return valves – Connected
	Flexible line – House
	Filter
	Cooler – With coolant flow line indication
	Air dryer

Example: Knowing the output force required (200 kN) and the pressure of the system (160 bar), connect Output force through pressure to cut cylinder diameter.

Answer: 125 mm.

To find the maximum length of a piston rod. Connect output force required (200 kN) through rod diameter (70 mm) to cut the maximum rod length scale; this gives you the (Lm) dimensions.

Answer: 2800 mm.

To find the actual length stroke (LA) for a specific mounting use formulae below.

Maximum stroke lengths for specific mounting cases

For intermediate trunnion positions scaled multiplier factors must be taken. Clevis and spherical eye mountings have the same factor as eye mountings.

Example: Having found Lm (2800 mm) for rear flange mount with eye rod end LA = Lm × 0.4 = 2800 × 0.4 = 1120 mm.

Source: Page 16 BFPA data book.

Seals

For full details of seal compatibilities, see ISO 6072: Hydraulic fluid power, compatibility between elastomeric materials and fluids or BS 7714: Guide for care and handling of seals for fluid power applications. For recommendation of O-ring seal standards, see BFPA/P22 ‘Industrial O–ring Standards – Metric vs Inch.'

Source: Pages 18–20 inclusive, BFPA data book.

Fluid cleanliness

The presence of particulate contamination ('dirt') is the single most important factor governing the life and reliability of fluid power systems. Operating with clean fluids is essential. Advice on contamination control can be gained from guide line document BFPA/P5.

Pump pulsation

Pump pulsation and Formula to size accumulator to reduce pump pulsations.

(a) Minimum effective volume (l) $V_1=\frac{k\cdot Q}{n}$
Note: It is good engineering practice to select an accumulator with port connection equal to the pump port connection.

(b) To check the level of pulsation obtained.
Volume of fluid entering accumulator = D · C
For pulsation damping precharge pressure P₁ = 0.7 · P₂ and assuming change from P₁ to P₂ is isothermal, then V₂ = 0.7 · V₁

$\begin{array}{l}{V}_3=V_2-(D\cdot C)\\ P_3=P_3{\left(\frac{V_2}{V_3}\right)}^{1.4}\end{array}$

Hence: Percentage pulsation above and below mean is $\left(\frac{P_2-P_3}{P_2}\right)100$

The tank cools the oil through radiation and convection.

$P=\frac{\Delta T_1\cdot A\cdot k}{1000}$

where:

k = 12 at normally ventilated space

24 W/m² °C at forced ventilation

6 at poor air circulation

Required volume of water flow through the cooler:

$Q=860\times \frac{\text{power loss}}{\Delta T\text{water}}1/\text{h}$

Heating

Heating is most necessary if the environmental temperature is essentially below 0°C.

Requisite heating effect:

$P=\frac{V\cdot \Delta T_2}{35\cdot \Delta t}\text{in kW}$

Energy

$J=M\cdot C\cdot \Delta T$

where:

M = Mass (kg)

C = Specific heat capacity J/kg°C

ΔT₁ = temperature difference (°C) fluid/air

ΔT₂ = increase in fluid temperature (°C)

Δt = time (min)

Note: 1 MJ = 0.2777 kW/h.

Heat equivalent of hydraulic power

$\text{kJ}/\text{s=}\frac{\text{flow (I/min)}\times \text{pressure}(\text{bar})}{600}=\text{kW}$

Change of volume at variation of temperature

Change or volume ΔV = 6.3 × 10⁻⁴ · V · ΔT

Change of pressure at variation of temperature

Note: With an infinite stiff cylinder.

Change of pressure Δp = 11.8 · ΔT (in general, affected by many variables)

Example: The temperature variation of the cylinder oil from nighttime (10°C) to daytime/solar radiation (50°C) gives:

$\Delta P=11.8\times 40=472bar$

Key

ΔT = temperature change (°C)

P = power (kW)

k = heating coefficient (W/m² °C)

A = area of tank excluding base (m²)

Δt = time change (min)

Δp = change in pressure (bar)

C = specific heat capacity (J/kg°C)

V = volume (l)

Source: Page 22 BFPA data book.

ISO 6538/CETOP RP50P method

Source: Page 23 (part) BFPA data book.

Mode of action

Three basic types

• Single-acting, spring return: Movement and force by air pressure in one direction, return movement by internal spring force, usually sprung to outstroke position but occasionally the reverse is available.

• Double-acting: Air pressure required to produce force and movement in both directions of travel.

• Double-acting, through rod: Double-ended piston rod which acts as a normal double-acting cylinder, but mechanical connections can be made to both ends of through rod.

Source: Page 23 (part) BFPA data book.

Rodless cylinders

Where space is at a premium and there are potential loading and alignment problems, a variety of rodless cylinder designs are available. The range of available bore sizes is limited (e.g. 16–100 mm).

Quality classes

Basically three qualities of unit available

• Light duty and compact cylinders: Limited range of bore sizes, up to 100 mm. Not cushioned at stroke ends, or cushion pads only. Check manufacturers data sheets for serviceability and susceptibility to corrosion.

• Medium duty/standard: For normal factory environments. Some degree of corrosion resistance. Serviceable. Cushioned at both ends. Usually double-acting. Bore size range, 32 mm and greater.

• Heavy duty: Rugged construction. Serviceable. Non-corrodible materials. superior cushioning, thicker piston rods and heavy duty mountings. Bore size range 32 mm and greater.

For interchangeability and standard mounting dimensions, see ISO 6432, 8–25 mm bore, ISO 6431, 32–320 bore: standard duty, double-acting, metric dimensions.

Standard bore sizes

• Double-acting: 8, 10, 12, 16, 20, 25, 32, 40 50, 63, 80, 100, 125, 160, 200, 250 and 320 mm.

Standard, stocked strokes

• Double-acting: 25, 50, 80, 100, 125, 160, 200, 250 and 320 mm.

Cylinder thrust

To calculate the theoretical thrust of a double-acting cylinder, use the formula:

• 

$\text{Thrust }=\left(\frac{\pi D^2\times P}{4}\right)\text{Newton}$

where D = diameter of piston (mm), P = Gauge pressure (bar).
Pull will be less, due to area of piston rod.

• 

$\text{Pull}=\left[\frac{\pi (D^2-d^2)\times P}{4}\right]\text{Newton}$

where d = diameter of piston rod (mm).

For static loading, that is, where full thrust is only required when the cylinder comes to rest (e.g. clamping), use the above calculation.

For dynamic loading, that is, where thrust is required throughout the piston travel, allowance has to be made for the exhaust back-pressure, friction, changes in driving pressure, etc., add 30% to the thrust figure required, for normal speeds. For higher speeds add as much as 100%.

Cylinder speeds

With normal loading, valving and pressure: 5–7 bar, the important factor is the relationship between the bore area of the cylinder and the actual bore area of the cylinder inlet ports. Conventionally this is in the order of 100:1 and would result in speeds of 0.3–0.5 m/s. For normal speeds, use a directional control valve and piping of the same size as the cylinder ports. For higher speeds use a cylinder of larger bore size than necessary plus larger valve and pipework but be careful of cushioning problems.

Stroke lengths

For static loading use any convenient standard, stocked stroke length as cushioning is not important. For dynamic loading, order the correct required stroke length as the use of external stops affects cushioning potential.

With long stroke lengths, that is, more than 15 × bore diameter, care must be taken to avoid side-loading on bearing, etc., use pivot type mountings. Check diameter of piston rod to avoid buckling under load. If necessary use a larger bore size cylinder than normal as this will probably have a longer bearing and a thicker piston rod.

Some miniature pneumatic components and heavy duty valves employ metal to metal sealing. Most equipment uses flexible seals manufactured from synthetic rubber materials. These are suitable for ambient temperatures up to 80°C. Fluorocarbon rubber os silicon rubber (Viton) seals are used for temperatures up to 150°C.

Synthetic seals are resistant to mineral-based hydraulic oils but specific types of oil must be checked with the equipment manufacturer to avoid problems arising from additives (see Section 5.6.12).

Good wear resistance ensures a reasonable performance, even with a relatively wet and dirty air supply. However, to ensure safe operation, with a satisfactory service life, system filtration and some form of lubrication is necessary.

Filtration

Good filtration starts at the compressor with correct siting of the air intake and an intake filter. Error sat this stage cause problems throughout the subsequent installation. After coolers and dryers ensure that the supply enters the ring main in good condition, but condensation and dirt can be picked up on the way to the point of use. Individual filters are necessary at each major application point.

For general industrial purposes, filters with a 40 µm element are satisfactory. For instrument pneumatics, air gauging, spraying, etc., a filter of 5 µm or better is required. High quality filters are often called coalescers. Filters are available with manual, automatic or semi-automatic drain assemblies.

To alleviate the problem of dirt entering open exhaust ports use an exhaust port silencer which also avoids noise problems. Simple exhaust port filters are also available, which offer a reasonable level of silencing, with little flow resistance.

Lubrication/modern equipment is often designed to run without lubrication

However, most industrial air supplies contain a little moisture. All pneumatic components are greased on assembly, unless specifically requested otherwise. This provides significant lubrication and ensures that the equipment performs satisfactorily for several million cycles, particularly if used frequently.

An airline lubricator is included in many industrial applications.

Conditioning units

It is estimated that 90% of failures in pneumatic systems are due to poor quality of the air supply. Contamination is drawn in at the compressor from the atmosphere. The level of contamination is effectively concentrated by the compression. Any contamination will attack the system components.

Modern pneumatic systems will include some form of air conditioning unit comprising a dryer to remove moisture, a filter to remove contamination and perhaps a form of lubrication.

Every application requires careful consideration on the type of conditioning to specify to meet the required operating condition.

Source: Page 26 BFPA data book.

Types of compressor

• Displacement compressors: Air is compressed by contracting the space containing air taken in at atmospheric pressure (e.g. reciprocating compressors – piston or diaphragm type; rotary compressors – sliding vane, gear, screw). Roots blower.

• Dynamic compressors: Compression is achieved by converting the air inlet rate into a pressure (e.g. centrifugal compressors – radial impeller, blade type, axial compressors).

Overlap occurs between the various types in terms of capacity and pressure range but some generalisation can be made. Use reciprocating compressors if very high pressures, up to 1000 bar are required. Rotary vane types are used for medium pressures, up to 7 bar and low capacity. Blowers are used for large volumes of low pressure air, up to 1 bar.

Sizes

For industrial applications compressors can be classified:

Small – up to 40 l/s

Medium – 40 to 300 l/s

Large – above 300 l/s

Installation

Three types of installation dependant on application:

• Portable: Paint spraying, tyre inflation, etc.

• Mobile: Road/rock drills, rammers, emergency stand-by sets, etc.

• Fixed: Machines, factory, workshop, etc.

Prime movers

Selection of correct drive unit is essential to obtain efficient and economical supply. Three basic types – Electric motors are used for compactness and ease of control; IC engine (diesel, petrol, gas) for mobile units, emergency stand-by sets or where an electrical supply is not available; Turbine (gas, steam) can be incorporated into the total energy system of a plant using existing steam or gas supplies.

Selection factors

• Delivery pressure: Must be high enough for all existing and potential future requirements. If there is a special requirement for a large volume of either high or low air pressure, it may be better to install a separate unit for that purpose.

• Capacity: Calculate not only the average air consumption but also maximum instantaneous demands, for example, large bore cylinders and air motors, operating at high speeds. Determine use factors. Frequently users add to existing airlines indiscriminately and run out of air.

• Intake siting: Intake air should be as clean and as cold as possible for maximum efficiency.

• Intake filter: High capacity to remove abrasive materials which could lead to rapid wear.

• Air quality: Study air quality requirements throughout the system or plant. The correct combinations of separators, aftercoolers, outlet filters and dryers should be determined. The problem of water removal should not be left to the airline filters associated with individual plant and systems.

• Stand-by capacity: What would happen in an emergency or when an individual compressor requires servicing.

• Air receiver: The system must have adequate storage requirements, not only to meet demand, but also to ensure efficient running of the prime mover.

• Air main capacity: A large bore ring main acts as a useful receiver, reduces pressure drops and operating costs. The cost of larger size of pipework is only a small proportion of the installation costs.

Source: Page 26 BFPA data book.

Air quality

ISO 8573-1 specifies quality classes for compressed air. A class number is made up from the individual maximum allowable contents of solid particles, water and oil in air, and can be used to specify air quality for use with valves and other pneumatic applications.

For general applications where ambient temperature is between +5°C and +35°C, air quality to ISO8573-1 class 5.6.4 is normally sufficient. This is 40 µm filtration, +10°C maximum pressure dew point and 5 mg/m³ maximum oil content. Pressure dew point is the temperature to which compressed air must be cooled before water vapour in the air starts to condense into water particles.

Air consumption

For cylinders with the bore and rod sizes shown, the values of consumption are for an inlet pressure of 6 bar and only 1 mm of stroke. To find the consumption for a single stroke or one complete cycle take the value from the appropriate column and multiply by the cylinder stroke length in mm. To adjust the value for a different inlet pressure divide by 7 and multiply by the required (absolute) pressure (e.g. gauge pressure in bar +1).

Cylinder forces

The theoretical thrust and pull is related to the effective piston area and the pressure. The tables show the theoretical forces in Newton for single and double-acting cylinders at

Table of air consumption.

Table of thrust and pulls, single-acting cylinders.

Table of thrust and pulls, double-acting cylinders.

6 bar inlet to the cylinder. For forces at other pressures divide the figures by 6 and multiply by the required pressure in bar gauge.

Load and buckling

For applications with high side loading, use pneumatic slide actuators or standard cylinders fitted with guide units. Alternatively external guide bearings should be installed.

When a long stroke length is specified, care must be taken to ensure the rod length is within the limits for prevention of buckling. The table shows the maximum stroke length for a variety of installation arrangements.

Valve flow

There are a variety of standards and methods for the measurement and display of valve flow performance. These can give rise to confusion and difficulty when comparing the published performance of different valves. The table below provides conversion factors as a guide to expressing valve performance in different units.

Flow factor conversion table

How to use

Select the unit of measurement that is known in the left hand column and multiply by the factor given in the column of the required unit of measurement:

'Cv’ is specified by ANSI/NFPA.

'Kv’ used in Germany and based on water flow.

'C’ sonic conductance in dm³/s/bar specified by ISO 6358.

'A’ effective area in mm² specified by ISO 6358.

'S' effective area in mm² according to the Japanese standard JIS B 8375.

A further measurement is the NW value. This gives the equivalent diameter in mm² of the smallest path through a valve. This is non-comparable and not in the table.

Lubricants

When to lubricate, via an oil-fog or micro-fog lubricator, is generally explained in this catalogue. However, the oil recommended is very much dependant on the local conditions and not least availability of various brands and labels.

In each country Norgren can recommend equivalent products, based on the information from the suppliers.