Convum Vacuum Generators Technical Details

Historically, Vacuum generators operated with compressed air have been an economical solution for material handling and pick&place applications. Convum's durable construction are efficient, cost effective, and virtually maintenance free. Each CONVUM generator is still handmade and 100% tested forvacuum flow, degree of vacuum, blow-of, and response time before leaving the factory.

DEFINITION: The CONVUM vacuum generators are based on the Venturi Principle. All vacuum generators mentioned on this site are to be considered venturi type.

SPACE REQUIREMENTS: CONVUM manufactures small, lightweight single stage venturi's to suit your application. Details of the smallest (CVS) to the largest (CVK) can be found in the Generator Section of this site.

AIR CONTROLS: CONVUM CV, MCA, and CV-VR require separate air control valves to operate. If cycle times or blow-off release requires integrated valving for fast response, consider the CVS, MC2, CVR-2, or CVK models. Typically, cycle times of 1 second or less may require integrated vacuum solenoid valve and release valve for blow-off.

PART PRESENCE: There are many applications for sensors; part presence, monitoring, or circuit controls. CONVUM manufactures a variety of sensors with digital switch outputs (125mA, 30VDC), analog outputs (1-5VDC), and current outputs (4-20mA). All CONVUM sensors are exceptional for applications requiring accurate and fast response. Accuracy resolution and accurate repeatability are critical to the overall performance of the system. Details of sensors compatible with generators or remote capabilities can be found in the Sensor Section of this site. MC2, CVR-2, CVK, and CV-VR generators offer integrated sensors as an option.

VACUUM LEVEL: Typically non-porous work pieces require high levels of vacuum ("H" series - High vacuum) and porous work pieces require a higher vacuum flow rate ("L" series - Low vacuum) and lower levels of vacuum. Evaluate the work piece characteristics to determine the type of vacuum required for your application.

For a vacuum level other than "H" (27inHg) or "L" (17inHg) series, select a CONVUM CVR-2 or CVK generator with a non-return check valve and an MPS-2 Digital output sensor. To control the level of vacuum, the sensor output operates the normally closed vacuum solenoid valve on the CVR-2/CVK. The sensor output (normally closed state) opens the vacuum solenoid valve until the programmed level of vacuum is achieved. The non-return check maintains the vacuum level. If leakage occurs, the adjustable hysteresis range of the output can be set to restore vacuum to the maximum programmed level. This circuit is well suited for material handling of glass or sheet metal, leak tests, or simple air-economizing.

Shown are the wiring diagrams for the CVR-2 and CVK generators operated in the air-conservation, blow-off guarantee, and part presence or preventative maintenance modes. The sensor outputs energize and de-energize the 3-way vacuum valve or blow-off valve by programming the switch point levels on the sensor display.

ELECTRICAL CONNECTIONS: Most valving is available for MC2, CVK, CVR-2, and CVS units in 24VDC or 110VAC. The basic connectors for these valves are described as grommet lead (G), push in clip type with LED lamp and surge suppression (L), or DIN ISO type (D).

FILTRATION: In general, filtration between the pad and generator is recommended. CONVUM provides filtration on the generator for additional protection. The units are MC2, CVR-2, and CVK. See the Filters Section for information on inline filters.

AIR CONSUMPTION: Each nozzle diameter requires a specific amount of available (scfm) to efficiently operate and achieve the specifications listed on this site. The required air supply (scfm) will vary by generator series and nozzle diameter. Air consumption (scfm) is listed for each specific generator on this site. This could influence the selection of the nozzle diameter. If the vacuum level drops during operation, consider increasing the supply pressure and tubing ID on the air supply.

RESPONSE TIME: With minimal leakage, and without time restraints, any vacuum source can reach the rated vacuum degree. The response time is important to the operation of the system, which will vary by the generator nozzle diameter and the total volume of air to be evacuated from the system. The response time (RT) calculation below is derived from actual test data relative to the rated vacuum flow rates of the Convum generators. All calculations are in metric units of measure. Charts with metric conversions have been provided.

RT(sec) = time for attaining vacuum (vacuum response time)
C = constant relative to vacuum degree
a = index relative to different types of the CONVUM
V_D = volume of air to be displaced in liters

V_D = 0.780 x ID² mm x Lm/1000 + P_v (n)
P_v = Pad volume in liters. n = Number of pads.

Nozzle	Vac. Flow	C		a
Ø	l/min / scfm	17 inHg	27 inHg	a
05HS	6 / 0.21		0.03	1.02
05LS	9 / 0.31	0.11		1.06
07HS	11 / 0.38		0.06	1.02
07LS	19 / 0.67	0.31		1.02
09HS	15 / 0.52		0.07	1.09
09LS	21 / 0.74	0.37		1.09
10HS	27 / 0.95		0.12	1.09
10LS	36 / 1.27	0.25		1.09
15HS	63 / 2.20		0.25	1.00
15LS	95 / 3.30	0.74		1.09
20HS	110 / 3.80		0.62	1.09
20LS	165 / 5.80	1.00		1.09
25HS	160 / 5.60		0.69	1.00
25LS	250 / 8.80	3.27		1.00
30AHS	225 / 7.90		0.97	1.00
30ALS	350 / 12.30	4.88		1.00

EXAMPLE: Calculate the response time of a Convum generator with a specific nozzle diameter and specific volume of air (V_D) to be displaced from the vacuum system.

25HS Nozzle Diameter = 2.5mm, Vacuum Flow 160 l/min (5.6 scfm), 27 inHg
Tube ID = 10mm, Tube Length = 3M, Pad = PBG-150mm = 0.26 L

Tubing Reference

Pad Volume Reference (P_v)

Tubing ID
SAE	mm
5/64	2.00
3/32	2.38
1/8	3.17
5/32	4.00
3/16	4.76
1/4	6.35
5/16	8.00
3/8	9.52
7/16	11.1

Tubing Length (L)
in.	M
18	.457
24	.610
30	.762
36	.914
42	1.07
48	1.22
54	1.37
60	1.52
66	1.67
72	1.82
84	2.13
90	2.28
108	2.74

PFG
Ø	in³	L
2	.00004	.0000006
3.5	.0001	.000002
5	.0003	.000005
6	.00048	.000008
8	.002	.00003
10	.004	.00007
15	.012	.0002
20	.03	.0005
25	.067	.0011
30	.067	.0011
35	.14	.0023
40	.18	.003
50	.25	.0042
60	.57	.0094
80	1.28	.021
95	1.95	.032
110	5.00	.082
150	10.80	.177
200	23.24	.381

PBG
Ø	in³	L
10	.013	.0002
15	.045	.0007
20	.070	.001
30	.28	.004
40	.56	.009
50	1.60	.026
75	4.63	.076
110	6.77	.111
150	15.86	.26

PCG
Ø	in³	L
5	.002	.00003
7	.003	.00004
10	.010	.0001
15	.060	.0009
18	.082	.001
20	.123	.002
30	.595	.009
40	1.15	.018
60	4.40	.072
90	10.0	.1639

SAE x 25.4 =mm

in. x 0.254=M

in³ x 0.01639 = Liters

VACUUM TUBING: Shown below are some unrestricted theoretical flow rates (SCFM) of tubing I.D. and length. When selecting vacuum tubing for the system, consider the flow rate of the tubing I.D. versus the vacuum flow rate of the generator. The tubing I.D. can affect the response time of the system. For a non-porous application, with minimal leakage, the ideal flow rate ratio of the vacuum generator flow capacity versus tubing I.D. flow capacity is 1:1. For applications where leakage is expected or faster response time is necessary select a vacuum generator which has a flow rate exceeding the tubing I.D. flow rate, or simply, adjust down the tubing I.D. But, if the vacuum tubing I.D. is too small, restricting vacuum flow, the vacuum generator may be considered inefficient. For porous applications where the leakage rate is considered excessive, consult with Convum. When using a manifold to distribute the vacuum to multiple vacuum pads, the flow rate on the main vacuum tubing to the manifold must be equal to or greater than the sum of the flow rates for each branch tubing to the pads to avoid restriction.

EFFECTIVE AIR FLOW OF TUBING (SCFM)
(Compare with Vacuum Flow Rates)
(Liters/Min. = SCFM / 0.035316)

AIR SUPPLY: Correct sizing of the supply line and solenoid valve, and air supply (C_v) is critical to the performance of the Convum generator. Refer to the chart below to select the proper supply line and supply valve (if necessary). If the vacuum level drops during operation, consider increasing the supply pressure and tubing ID on the air supply. In general, select solenoid valves with an effective sectional area three times greater than the sectional area of the nozzle diameter.