the principles of the present invention are particularly useful in a system generally indicated at 10 in the figure for controlling the emissions of solvents such as volatile organic compounds from a printing press generally indicated at 11 which includes a plurality of printing stations 12 1 , 12 2 , . . . 12 n . each of the printing stations 12 1 , 12 2 , . . . 12 n is provided with a drying hood or chamber 19 1 , 19 2 , . . . 19 n . each of the printing stations such as 12 1 has idler rolls such as 13 for guiding a web of material 14 between a roll 15 and a pressure roll 16 . the printing roll 15 receives a printing fluid or ink from a supply 17 . after passing through the rolls 15 and 16 , the web passes through a slot in a bulkhead or partition 18 which separates the printing station from the interior of the drying hood or chamber 19 . each of the drying chambers , such as the drying chamber 19 , has a plurality of rollers 20 for guiding and conveying the web in a u - shaped path so that it may be subjected to a flow of drying gases or air from a nozzle means diagrammatically illustrated at 21 . after passing through from the drying chamber 19 , the web passes back through another slit in the bulkhead 18 over an idler 22 to the next printing station such as 12 2 . to provide a flow of heated drying gases or air through the nozzle means 21 , a blower means 23 which may be a fan blower is provided and has an inlet 24 for receiving the gas or air to be passed through the nozzles . the actual construction of the nozzles and the necessary manifolds for the nozzle means may be that of the conventional drying hoods or that illustrated in u . s . pat . nos . 2 , 554 , 239 , 2 , 791 , 039 , and 2 , 932 , 092 , whose disclosures are incorporated by reference thereto . the system 10 includes a means or unit for removing the solvent from the air which is generally indicated at 30 . the unit or device 30 has an oxidation chamber 31 , which is interposed between two regeneration chambers 32 and 33 , which are pebble beds heat generators . in addition , the device includes an inlet means 34 which is in communication through a valve 35 with a header 36 for the regeneration chamber 32 and is in communication by a valve 37 with a header 38 for the regeneration chamber 33 . an outlet means 39 is in communication with the header 36 through closable valve 40 and with the header 38 through a closable valve 41 . briefly , the device 30 is constructed to receive exhaust gas from the dryers through the inlet means 34 which connected to pass the gas through the valve 35 to the header 36 and into the regeneration chamber 32 to be preheated before reaching the oxidation chamber 31 . in the oxidation chamber 31 , the volatile organic compounds are oxidized and the heated or oxidized gases are then conveyed through the regeneration chamber 33 for heating the pebble bed and then out through the valve 41 into the exhaust means 39 . in this form of operation , the valves 37 and 40 are closed . after a period of time , the valves 35 and 41 are closed and the valves 37 and 40 are opened so that the flow is in the opposite direction . the actual structure and a more detailed discussion of the operation of the device is contained in u . s . pat . no . 4 , 176 , 162 , whose disclosure is incorporated by reference thereto . the outlet means 39 is connected to an inlet for an output manifold 50 which has a plurality of discharged outlets 51 1 , 51 2 , . . . 51 n , an adjustable outlet 52 having a control means such as a valve 53 , and a terminal outlet 54 . as illustrated , the plurality of discharged outlets 51 1 , 51 2 , . . . 51 n are in communication with the gas inlets 24 1 , 24 2 , . . . 24 n , respectively . the terminal outlet 54 is in communication with a heat exchanger 55 which cools the gases from the output manifold 50 and discharges them into an exhaust manifold 56 through a flow control device illustrated as a valve 57 . the exhaust manifold 56 has a plurality of discharge outlets 58 1 , 58 2 , . . . 58 n , which are in communication with the gas inlets 24 1 , 24 2 , . . . 24 n , respectively . in addition , the manifold 56 has a plurality of exhaust inlets 59 1 , 59 2 , . . . 59 n which are in communication with the hoods 19 1 , 19 2 , . . . 19 n , respectively . finally , the exhaust manifold 56 terminates in a system fan 60 which creates a negative pressure in the exhaust manifold 56 , and a discharges into the inlet means 34 of the unit 30 . it is noted , that the exhaust manifold 56 includes an adjustable bleed orifice 61 , a fire damper 62 , and a replaceable filter 63 . it should be noted that each of the exhaust inlets 59 1 , 59 2 , . . . 59 n , includes valves or dampers such as 80 1 , 80 2 , . . . 80 n , which enable controlling the amount of negative pressure created in each of the hoods 19 1 , 19 2 , . . . 19 n , by the system fan 60 which forms means for creating a negative pressure in the chambers of the hoods . as illustrated , the inlet such as 24 1 is connected both to a discharge outlet 51 1 of the output manifold 50 and to a discharge outlet 58 1 of the exhaust manifold 56 . each of these outlets is provided with valve means such as a damper 71 1 for the outlet 51 1 and the damper 72 2 for the outlet 58 1 . by adjusting the positions of these dampers , the amount of gas that is pulled into the gas inlet 24 1 from each of the manifolds 50 and 56 can be adjusted to change the amount of mixture of the gas being directed through the nozzle means 21 by the blower means 23 . as pointed out hereinabove , when the heat exchanger 55 is provided , the temperature of the gas in the exhaust manifold 56 is below those of the output manifold 50 and therefore changing the percentage of the gas from each manifold being passed by the blower means to the nozzle means will vary the temperature . if desired , a temperature control such as 73 1 can be connected to operate the valves 71 and 72 in response to sensed temperature conditions . in addition , each of the exhaust inlets 59 1 , 59 2 , . . . 59 n is provided with an automatic control for the valve 80 1 , 80 2 , . . . 80 n which is connected to a control means 81 1 , 81 2 , . . . 81 n that is illustrated as a lower explosion limit ( lel ) control device . the arrangement of the valve 80 1 in the device 81 1 acts as a means to control lel to a preset level or a safety arrangement which will shut down the entire system should the concentration of the volatile organic compounds in the hoods such as 19 1 reach an undesirable maximum limit . the structure and operation of the lel control is described in greater detail in u . s . pat . no . 4 , 150 , 495 , and the disclosure of this patent is incorporated herein by reference thereto . the device operates in the following manner . starting with the outlet means for the device 30 , the cleaned up emissions of the device 30 which are at an elevated temperature have a portion which is passed through the various discharged outlets 51 1 , 51 2 , . . . 51 n , a second portion which is discharged through the outlet 52 to the atmosphere and a third portion which passes through the heat exchanger into the exhaust manifold 56 . thus , the air , that is being passed through the nozzle means in each drying hood , will be a mixture of air from the exhaust manifold plur air from the output manifold . after passing through the nozzle , the air or gas is then exhausted back into the exhaust manifold . while the air or gas in the exhaust manifold 56 will have a slightly higher concentration of the volatile organic compound , the concentration will not approach the concentrations of the prior art systems . as the gas in the manifold 56 is drying by the means for creating a negative pressure 60 , it is then passed into the device 30 which will oxidize the volatile organic compounds . as noted in the above mentioned u . s . pat . no . 4 , 176 , 162 , a minimum concentration is necessary for the oxidation in the chamber 31 to occur without the addition of fuel . in the present system , it is noted that this minimum percentage of the lel which is roughly 6 % lel will not be met and therefore the unit 30 will require the burning of fuel to maintain the oxidation in the chamber 31 . it should be noted that these units , such as disclosed in the above mentioned patents do have burners provided which enable them to operate when the gas being processed is below the self sustaining point of the oxidation chamber . in the present system for a given printing press site and location , one needs to know the following criteria . the number of printing stations being used and the maximum volume of volatile organic compounds which can be emitted to the atmosphere for a given period of time . the number of printing stations being used will establish the volume of air that must be returned to the atmosphere . while the volume per station may be varied slightly , it is usually about 500 scfm per station . by dividing the maximum volume of volatile organic compounds which may be released to the atmosphere by the volume of air that must be returned to the atmosphere , the maximum concentration of the volatile organic compounds in the &# 34 ; cleaned - up &# 34 ; air can be established . by multiplying this concentration by 10 or 20 , depending upon whether the basic clean up efficiency of the volatile organic compound reduction unit 30 is 90 % or 95 % will give the maximum concentration level of the volatile organic compounds in the flow of gas being delivered to the inlet means 34 of the unit 30 . finally by dividing the maximum volume of the volatile organic compounds required during a given period of time by the maximum concentration level or the volatile organic compounds would establish the constant volume of air that must be processed through the volatile organic compound reduction unit 30 which unlike conventional systems is treated as a constant volume unit with the volume of air processed through the unit being constant and independent of the contamination level of the input air . with the above information , the total air emitted through the system through the outlet 52 is controlled by the valve or adjustment means 53 . the fresh air entering the system primarily enters through the slots in the bulkheads such as 18 between the hood 19 and the printing units 12 . since a portion of the gases or air in the output manifold 50 is being discharged to the atmosphere , the amount of concentration of the volatile organic compounds in the gas in the output manifold 50 cannot exceed the concentration in the air being discharged to the atmosphere . while the present system will be less efficient with the consumption of energy due to the requirements of providing fuel in the oxidation chamber 31 to obtain the desired temperature for oxidation , the system will be able to meet the restrictions concerning the maximum amount of volatile organic compounds which are discharged to the atmosphere . it is possible to further refine the system by providing means for controlling the volume of air being processed through the system either by sensing the volatile organic compound levels in the air being returned to the environment or by measuring the volatile organic compound levels in the input means to the reduction unit 30 . although this would not eliminate the energy requirements , it should substantially reduce them . although various minor modifications may be suggested by those versed in the art , it should be understood that i wish to embody within the scope of the patent granted hereon , all such modifications as reasonably and properly come within the scope of my contribution to the art .