Definition :

      Vacuum means absence of matter, absence of gas or at least rarefied gas. In a volume under vacuum, the number of molecules present at a moment is lower than the number of molecules of this volume at the atmospheric pressure.
    This definition doesn’t allow to measure the size of the phenomenon; we chose a physical size proportional to the number of molecules: it is the pressure.
    We used to define the range of pressures lower than the atmospheric pressure from 105 to 10-12 Pa in several fields, with approximate limits .

Definition of atmospheric pressure

    In a given place, it is equivalent to the weight per area unit of the air column above this area. The official international unit is Pascal. The atmospheric pressure varies according to the location and the altitude where we are. On average, at the sea level, it is 1013 hPa.

Correspondence table of pressure units

    Concerning vacuum, for reasons of convenience, vacuum pressure is expressed in % of vacuum: in fact 85% of relative vacuum = 15% of absolute vacuum.
 

ABSOLUTE PRESSURE				RELATIVE PRESSURE			VACUUM PRESSURE
mbar	Pa	Psi	mm/Hg	% de vide	bar	mm/Hg	bar
1013	101300	14,41499	760,00325	0%	0,00	0,00	0
900	90000	12,807	675,225	11%	-0,11	84,78	0,113
800	80000	11,384	600,2	21%	-0,21	159,80	0,213
700	70000	9,961	525,175	31%	-0,31	234,83	0,313
600	60000	8,538	450,15	41%	-0,41	309,85	0,413
500	50000	7,115	375,125	51%	-0,51	384,88	0,513
400	40000	5,692	300,1	61%	-0,61	459,90	0,613
300	30000	4,269	225,075	70%	-0,71	534,93	0,713
200	20000	2,846	150,05	80%	-0,81	609,95	0,813
100	10000	1,423	75,025	90%	-0,91	684,98	0,913
0	0	0	0	100%	-1,01	760,00	1,013

    1 bar = 105 Pa = 1000 mbar = 750,25 mmHg = 14,23 Psi
    1 hPa = 1 mbar

Vacuum specific properties

The maximum pressure difference is of 1 bar in a vacuum circuit (between the absolute zero and the atmospheric pressure). Thus, be aware of :    SAPELEM vacuum generators are designed to save energy and to provide optimized vacuum around 0.8 bar. It is thus advisable to choose the vacuum generator suitable to your application and not to focus only on the maximum vacuum level. . SAPELEM and its distribution network are entirely at your disposal in order to help you to determine the best solution of vacuum generation.    Given the low difference of pressure, vacuum is particularly sensitive to the leaks and to the drops of loads.     It thus advisable to make sure of the circuit tightness and to choose the best hoses sections. . SAPELEM proposes a range of components particularly studied to take into account the vacuum specific properties.

Which vacuum pressure to choose?

Warning! Higher is the vacuum level,
• higher is the energy consumption,
• longer is the time to reach vacuum level,
• harder are the leaks to be compensated.

    So many reasons for not choosing systematically the higher vacuum level in a range of vacuum generators.

Your application	Vacuum pressure
	10%	20%	30%	40%	50%	60%	70%	80%	90%	99,5%
Handling
Porous and light products (cardboards, papers….)
Friable or fragile products (toasts, brioches….)
Very thin and deformable products (seals, containers….)
Handling of tight products (metal, plastic, glass….)
Pneumatic transport
Atmosphere control
Heavy products (steel balls…)
Air circulation
Atmosphere control
Tanks degassing
Ventilation of premises
Moulding
Resin desbubbling
Resin flow
Hold during
machining
sticking
forming

		Moderately suited
		Recommended

Correspondence table of flow units

l/s	l/mm	m3/mn	m3/h	cfm
1	60	0,06	3,6	2,12
10	600	0,6	36	21,2
20	1200	1,2	72	42,4
30	1800	1,8	108	63,6
40	2400	2,4	144	84,8
50	3000	3,0	180	106
60	3600	3,6	216	127,2
70	4200	4,2	252	148,4
80	4800	4,8	288	169,6
90	5400	5,4	324	190.8
100	6000	6,0	360	212
110	6600	6,6	396	233,2
120	7200	7,2	432	254,4
130	7800	7,8	468	275,6
140	8400	8,4	504	296,8
150	9000	9,0	540	318

1l/min = 0,016 l/s = 0,0001 m3/min = 0,06 m3/h = 0,0353 cfm

All the air flows mentioned in this website are expressed in free gas on the SRA conditions (Standard Reference Atmosphere) according to the ISO 8778 standard.

• The SRA conditions are: T = 20° C = 100 kPa (that is 1 bar) and 65 % of humidity.
• The flows on the SRA conditions are also noted Nl/min or Nm3/h.

The conversion between l/min and Nl/min is made thanks to the MARIOTTE BOYLE’s law:
PV = NRT that is PV/T = NR = cte
P = Absolute pressure
V = Volume
R = Constant of the perfect gases
T = Absolute temperature
N = Number of molecules in the volume


Example: a compressed air flow of 1000 litres/min at 2 bar and at 100° C corresponds to :
P1 = 2 bar = 2.10 5 Pa
V1 = 1000 l
T1 = 100° C = 273 + 100 K

P2 = 1 bar = 10 5 Pa
T2 = 20° C = 273 + 20 K
V2 = Volume calculated

P1V1 / T1 = P2V2 / T2
V2 = P1.V1.T2 / P2.T1
V2 = 2.105 x 1000 x 293 /105 x 393

V2 = 1570 Nl so a flow of 1570 Nl/min

Which flow to choose ?

The vacuum generator’s flow affects the draw off time of a given volume and the capacity to compensate leaks. It is thus advisable to make sure of the tightness and the dimensions of the vacuum circuits
• Single-stage vacuum generators are designed to provide vacuum or flow
• Multi-stage vacuum generators can provide both

	Flow
Your application	low flow from 1l/mn to 60 l/mn			Average flow from 100 to 500 l/mn			High flow from 500 to 3000 l/mn			Very high flow more than 1000 m3/h
Handling
Porous products (cardboards, papers….)						Only trials with samples can allow to choose the flow
Friable or fragile products (toasts….)
Very thin and deformable products (aluminium seals, plastic containers….)	Light products thus little suction cups and low flow generally
Handling of tight products (metal, plastic, glass….)	Time to bleed off a volume to vacuum is more important that the flow itself to keep up the pace
Pneumatic transport
Light products (polystyrene balls…)			Only trials with samples can allow to choose the flow
Heavy products (steel balls…)
Air circulation
Atmosphere control	Search for a constant flow
Tanks degassing								Depends of the volume of the tank or of the premises to be ventilated
Ventilation of premises
Moulding
Resin desbubbling
Holding during
machining
sticking
forming

Handling of tight products :
The best ratio suction flow/consumption is obtained with a vacuum level of nearly 80 %.
By experience, for a quick suction flow rate evaluation, see the chart below :
For a suction cup Ø < 40 mm, the suction flow = 8 Nl/min
For a suction cup Ø 40 to 75 mm, the suction flow = 15 Nl/min
For a suction cup Ø>75mm, the suction flow = 25 Nl/mn
Thus all you have to do is multiply the unit flow by the number of suction cups in order to obtain the recommended flow

Vacuum generation’s technology

SAPELEM offers two types of vacuum generators according to the used energy :
• Pneumatic vacuum generators
• Electric vacuum generators

Pneumatic vacuum

Pneumatic vacuum generators are also called venturis, ejectors, pneumatic vacuum pumps…The principle used by SAPELEM is known under the name of venture principle

• Single-stage vacuum generators :
  

          Based on the venturi principle, they are reliable and simple
            - no moving parts
            - no wearing
            - no servicing
            - no plugging

• • Multi-stage vacuum generators :
  

          Principle: several venturis are connected in series with flappers between each stage.

- High flow       - High vacuum level       - Air saving

• • In line vacuum generators :

Their design makes them particularly strong and insensitive to the presence of dusts or particles in the suction flow. They also can be used for applications of pneumatic and suction transportation (turnings, balls, dust…)

• • Additional equipment: multifunction vacuum generators :
  

    The venturis can be equipped with additional functions which make their integration into the modern automatisms easier.

- Nonreturn valve : Hold the part in case of vacuum generator supply failure = safety - On-Off : On distingue trois type de pilotage NO (Normally Opened) in case of lack of piloting (supply failure) the venture is turned on  NC (Normally Closed) in case of lack of piloting (supply failure) the venture is turned off Bistable, the venturi stays in the same state when the power cut. If it was turned on, it stays on. If it was stopped, it stays turned off =safety - Self-regulation : The venturi automatically stops when the vacuum level is reached and it restarts as soon as it’s necessary = air saving - Blow: Release very quickly the part in order to keep up high paces. There are two types of blow Piloted blow: blow is activated on receipt of an order; the time of blow is adjustable. Automatic blow: when the venturi off, a compressed air reserve bleeds off in the vacuum circuit; this little powerful blow is reserved for little vacuum circuits Vacuum level control Vacuum switch: sensor of electric, electronic or pneumatic vacuum level control Vacuumeter: Dial with pointer. Visual control of the vacuum level - Silencer Standard: works by baffle (2EJ.BL) or by porosity (2EJPL , 2EJR, 2EJMI°) Unpluggable: our HE silencers are particularly recommended for dusty or difficult applications. They offer the best soundproofing efficiency. They suit to all our range of vacuum generators.

In our SMX range, all these functions are included together in an extremely reduced size.

 

The compressed air passes through a calibrated hole (nozzle (1)), carries the air at the level of the suction hole (2) and generates vacuum. Supply and suction air are then exhausted through the hole (mixer (3)) to the silencer (4).

There are two principles to realize a vacuum network :

• Centralized network: one vacuum generator supplies several suction cups
• Individual network: each suction cup has its own independent vacuum generator.

 

Electric vacuum
    There are several technologies to generate vacuum by electric energy.
The application purpose will determine the choice of technology: examples  :

• Vacuum handling: Dry vanes pumps
• Resin desbubbling : Lubricated vanes pumps
• Medical vacuum and laboratories: Water rings pumps
• Handling of porous products, ventilation : Suction units

    
    • Working principle of an electric vacuum pump

The rotation of offset vanes respect to the stator produces an increase in volume which generates a vacuum pressure. The lubricated or dry vanes vacuum pumps allow to get significant flows with a high vacuum level

   
     • Working principle of a suction unit

The high- speed bucket wheel rotation generates the vacuum pressure by centrifugal effect. The suction units generate a very significant suction flow with a low vacuum pressure

Which vacuum generation technology to choose ?

	Pneumatic Generators		Electric Generators
Characteristics	Single-stage	Multi-stage	Electric
Purchase price	▲▲▲	▲▲
Cost of energy	▲	▲▲	▲▲▲
Low servicing	▲▲▲	▲▲
Robustness	▲▲▲	▲▲▲	▲
Explosion proof	▲▲▲	▲▲▲	▲
Compact	▲▲▲	▲▲
Lightness	▲▲▲	▲▲
High suction flow	▲	▲▲	▲▲▲
High vacuum level	▲▲	▲▲	▲▲▲

  Legend : ▲▲▲ Very good  ▲▲ Good ▲ Mean