SECHRIST 3500 (01) PDF Document

The SECHRIST 3500 Air-Oxygen Mixer is a restricted medical device intended for use only by qualified personnel under the direction of a qualified physician. Personnel operating this equipment are responsible for reading and thoroughly understanding all product documentation provided.

The mixer will perform in conformance with the specifications when assembled, operated, maintained, and repaired in accordance with the provided instructions. Do not attempt to operate this mixer before reading and thoroughly understanding these instructions. The mixer must be checked periodically as specified in the manual. A defective device should not be used.

This product should be repaired only in accordance with written instructions from SECHRIST, and should not be modified in any way, except with prior written approval from SECHRIST.

WARNINGS:

• Whenever a patient is attached to respiratory care equipment, constant attendance is required by qualified personnel. The use of an alarm or monitoring system does not give absolute assurance of warning for every form of malfunction that may occur with the system. In addition, some problems may require immediate attention.

• This precision gas mixing device is intended for use with Medical Breathing Air and Medical Breathing Oxygen only. Do not modify inlets to accommodate other breathing gases, especially anesthetic gases.

CAUTIONS:

• Federal law restricts this device to sale by or on the order of a physician.

• Grasp nipple at base next to the proportioning valve block – not on the end or the nipple may be damaged.

• If resistance is met before stop pin at 1.0 position is reached, do not force the knob. Re-adjust rear seat slightly – just enough to allow free range of movement to stop pin position. Recheck the calibration as described.

• Alarm bleed set screw (P/N 3568) is calibrated at factory and should not require calibration.

• Do not tape or hold finger over alarm outlet port. Permanent damage to reed can be caused by prolonged occlusion of reed outflow.

• DAMAGE MAY OCCUR TO BOTH FRONT SEAT AND REAR SEAT, WHEN REAR SEAT IS BEING INSTALLED, IF NEEDLE IS NOT STRAIGHT UP AND CENTERED.

• DO NOT ATTEMPT TO DIG BALL OUT OF HOLE: DAMAGE WILL OCCUR.

• DO NOT IMMERSE THE MIXER. DO NOT GAS OR STEAM STERILIZE; DAMAGE MAY RESULT.

The Maintenance, Repair, and Testing procedures covered in this manual are to be performed by individuals qualified in the servicing and maintenance of medical life support equipment. ONLY procedures covered in this manual are to be performed in the field. Procedures requiring more extensive electronic/pneumatic trouble-shooting, and/or electronic component replacement must be performed by Sechrist Industries, Inc.

FIO2 RANGE:	.21 ±.01 to 1.0 ±.01
ACCURACY*:	±3%
MAXIMUM FLOW:
Model 3500 (Low Flow):	40 LPM @ .60 FIO2 setting with 50 p.s.i. (@ 1.5 SCFM minimum flow) inlet pressures
Model 3500HL (Hi/Lo Flow):	100 LPM @ .60 FIO2 setting with 50 p.s.i. (@ 1.5 SCFM minimum flow) inlet pressures
NOMINAL SUPPLY PRESSURES**:	50 p.s.i. ±10 p.s.i. (@ 1.5 SCFM minimum flow).
BLEED FLOW:
Model 3500 (Low Flow):	3.0 to 4.0 LPM @ 7 LPM Flow
Model 3500HL (Hi/Lo Flow):	7.5 to 9.5 LPM @ 15 LPM Flow
DIMENSIONS:
Model 3500 (Low Flow):	HEIGHT: 6″ WIDTH: 6″ DEPTH: 6″
Model 3500HL (Hi/Lo Flow):	HEIGHT: 6″ WIDTH: 6″ (Pole Mount), 6 1/2″ (Wall Mount) DEPTH: 6″ (Pole Mount), 5 1/2″ (Wall Mount)
WEIGHT:	6 lbs.

*NOTE: The Mixer will maintain the delivered FIO2 within ±1% of the selected value with fluctuations of the supply pressures. The additional 2% error is caused by the readability of the set point and scale error.

**NOTE: The outlet pressure of the Mixer will always be slightly lower than the lower of the two inlet pressures. Some respiratory care equipment attached to the Mixer may require closer tolerances; consult the manufacturer’s instructions.

Use the following guide to identify the possible cause and correction for issues with your SECHRIST 3500.

PROBLEM	POSSIBLE CAUSE	CORRECTION
PROPORTIONING MODULE
FIO2 not accurate	O2 analyzer out of calibration (most common problem)	recalibrate O2 analyzer
	Improper purity of supply gases	Check quality of supply gases
	Wrong gas supplied to inlet	Assure outlets and hoses are correct
	Front or rear seats worn	Clean or replace seats
	Calibration of proportioning valve incorrect	See Calibration Section
	Pressure Balancing Module malfunctioning	See Calibration for Pressure Balancing Module
Knob is hard to turn	Faceplate has shifted causing knob to rub	Reposition faceplate
	Knob has been bumped bending adjustment shaft	Replace adjustment shaft and recalibrate
PRESSURE BALANCING MODULE
FIO2 Change > 1% when testing	Air or O2 inlet filter dirty causing >20 p.s.i. difference	Replace filter
	Regulator needle(s) out of calibration	Calibrate
	O-ring(s) on regulator seat damaged causing leak	Replace O-rings and recalibrate
	Contamination from supply gases	Clean and recalibrate
ALARM MODULE
Continuous alarm with both inlet pressures equal	Dirty inlet filter(s)	Replace filter(s)
	Bypass check ball leaking	Need to clean check ball and seat (see Disassembly of Alarm Module)
	Alarm Module adjustments out of calibration	See Calibration Section
Alarm not sounding with loss of one pressure	Defective reed	Replace reed
	Alarm Module adjustments out of calibration	See Calibration Section
	Alarm poppets stuck	Clean, lubricate and recalibrate

1.0 Initial Test System Set Up

1.1 Connect the Mixer to clean and dry Medical Breathing Oxygen and Medical Breathing Air supplies which are independently adjustable from 0 to 60 p.s.i.

1.2 Connect a flowmeter to the outlet of the Mixer.

1.3 Direct the flow from the flowmeter to a sampling reservoir (i.e. bottle or tube), making sure that no room air is being entrained to dilute the mixture.

1.4 Insert O2 analyzer probe into sampling reservoir. NOTE: O2 analyzer must be calibrated and accurate to ±1%.

1.5 The sampling rate should be: 7LPM for Low Flow, 15 LPM for Hi/Low Flow.

2.0 Proportioning Module Test

2.1 Set O2 pressure and air pressure to 50 p.s.i.

2.2 Compare O2 analyzer readings to Mixer settings of .21, .40, .60, .80 and 1.0.

2.3 The Mixer has a specified accuracy of ±3%. If the FIO2 varies more than ±4% between the Mixer and O2 analyzer reading, calibration or service may be necessary (see Troubleshooting Guide).

2.4 There is a constant bleed of mixed gas from the bottom of the Proportioning Module. This bleed is approximately 3 1/2 LPM for Low Flow and 8 1/2 LPM for Hi/Lo Flow. This is needed to maintain accurate FIO2s at very low flows. These bleed rates are predetermined by the factory and cannot be reset in the field.

3.0 Pressure Balancing Module Test

3.1 With same test system set up as above, select an FIO2 of .60 and observe the O2 analyzer reading.

3.2 Vary the inlet pressures to the Mixer to 40 p.s.i. O2 and 60 p.s.i. air and then to 60 p.s.i. O2 and 40 p.s.i. air. If FIO2 varies more than ±1% from initial O2 analyzer reading, calibration or service may be necessary (see Troubleshooting Guide).

4.0 Alarm Module Test

4.1 Set air and O2 supplies to 50 p.s.i.; alarm should be silent.

4.2 Slowly reduce air inlet supply; the alarm should sound between 24 and 28 p.s.i. and O2 analyzer should read 100%. Increase air inlet supply, slowly, to 50 p.s.i.; alarm should reset at or before 40 p.s.i.

4.3 Repeat step 4.2 varying the O2 inlet supply; when alarm sounds, O2 analyzer reading should be 21%.

4.4 If alarm does not function as per above specifications, calibration or service may be necessary (see Troubleshooting Guide).

5.0 Air Inlet Filtration System Test

5.1 To test the pressure drop through the water/trap filter or the internal air inlet filter, a test port has been provided on the rear of the Mixer above the air inlet.

5.2 With 1/4″ nut driver, remove plug from test port and install a Brass 10-32 x 1/16 fitting (P/N IV-310) (see Tool Kit).

5.3 Connect a high pressure gauge (0 to 60 p.s.i.) to 10-32 fitting.

5.4 With flow set at 7 LPM for Low Flow (15 LPM for Hi/Lo Flow), set mixer knob to .21. Observe pressure indicated at test port.

5.5 If the difference between the pressure at the test port and the inlet pressure is greater than 10 p.s.i., replace either or both air inlet filters (see Routine Maintenance section).

To calibrate the SECHRIST 3500, the system must be broken down into 3 modules. The order of calibration must be followed:

1. The Pressure Balancing Module must be calibrated before the Proportioning Module can be connected and calibrated.

2. The Pressure Balancing Module and Proportioning Module must be calibrated together before the Alarm Module can be installed and calibrated.

1.0 Pressure Balancing Module Calibration

1.1 To calibrate the Pressure Balancing Module, all accessory parts and the Proportioning and Alarm Modules must be removed.

1.2 Using a 3/16″ allen wrench, remove 4 screws from the air block and divide the module into 3 sections: air block, oxygen block, and diaphragm assembly.

1.3 Using a precision caliper, measure the thickness of the diaphragm assembly. The distance should be about 0.800 ± 0.010.

1.4 Locate the measured diaphragm thickness in the Regulator Needle Setting Table to find the corresponding depth micrometer setting.

1.5 Set the depth micrometer to the setting indicated in the table; rest the micrometer across the block cavity.

1.6 Using a 1/16″ or 5/64″ allen wrench, loosen the set screw. Using Assembly Tool 1, insert into the eccentric adjuster and begin turning clockwise.

1.7 The regulator seat and needle will move up and down. Calibration must be done on the downstroke.

1.8 As the spanner wrench is turned clockwise, the needle and seat will reach top dead center and start back down. As it starts down, slide the depth micrometer back and forth across the needle.

1.9 Slowly turn the spanner wrench in small increments. Listen for the tapping noise of the micrometer contacting the needle.

1.10 At some point in the downstroke, the micrometer will no longer contact the needle. As soon as the tapping noise ceases, the regulator needle is in the proper position.

1.11 Using a 1/16″ or 5/64″ allen wrench, tighten the set screw to secure calibration.

1.12 Calibrate both blocks in this manner and reassemble the Pressure Balancing Module. Position the 2 halves so that they are flush.

1.13 Tighten the 4 screws in a cross pattern to evenly distribute pressure.

2.0 Proportioning Module Calibration

2.1 Attach the Proportioning Module to the Pressure Balancing Module. Be sure O-rings are in place.

2.2 Install the faceplate.

2.3 Install Assembly Tool 4 to occlude high pressure inlet ports to the Alarm Module.

2.4 Using needle nose pliers, remove the bypass nipple.

2.5 Install the brass plug into the bypass nipple port.

2.6 Install a flowmeter.

2.7 Connect Medical Breathing Air and Medical O2 supplies.

2.8 Connect proportioning output to a calibrated O2 analyzer.

2.9 Set the flow to 7 LPM (Low Flow) or 15 LPM (Hi/Lo Flow) to the O2 analyzer.

2.10 Turn the adjustment shaft by hand until the O2 analyzer reads 30%.

2.11 Attach the Mixer knob to the adjustment shaft, aligning the black indicator on the knob with the 30 position on the faceplate. Lightly tighten the set screw.

2.12 Turn the knob to the 90 position; check the O2 analyzer reading.

2.13 Using AT. 3, loosen the jam nut. Using AT. 2, adjust the rear seat until the O2 analyzer agrees with the knob reading of .90 ± 1%.

2.14 Turn the knob to the .21 position (hitting the stop pin), then up to the .30 position. The O2 analyzer should read 30±1%. If necessary, rotate the knob until a reading of 30±1% is obtained, and reposition the knob to align the indicator with the .30 position.

2.15 Turn the knob to the .90 position; adjust the rear seat until the O2 analyzer reads 90±1%.

2.16 Repeat steps 2.14 and 2.15 until proper readings are recorded.

2.17 Turn the knob to the 1.0 position; make sure the O2 analyzer reads at least 98% (no higher than 99.5%) and the knob is hitting the stop pin.

2.18 Using AT. 3, tighten the jam nut to secure the calibration of the rear seat.

2.19 Verify that the full range of positions can be obtained within a ±3% variation.

2.20 When calibrations are completed, tighten the knob set screw(s).

2.21 Turn gas supplies “OFF”, remove the bypass plate, and install the bypass nipple.

3.0 Alarm Module Calibration

3.1 Slide the Alarm Module onto the bypass nipple and secure it to the Pressure Balancing Module. Be sure O-rings are in place.

3.2 Test alarm bleed response: turn O2 valve “ON” to 60 p.s.i., leave air “OFF”; the alarm should sound. Turn O2 down to 30 p.s.i.; the alarm should sound. If it sounds throughout this range, the alarm bleed is functioning.

3.3 If the alarm is not functioning properly, check the reed. If alarm bleed calibration is needed, follow steps for adjusting the alarm bleed set screw.

3.4 To calibrate the bypass alarm O2 calibration adjuster, turn O2 and air to “ON”, regulating to 50 p.s.i. The alarm should be silent.

3.5 Using gas supply regulators, set air supply to 50 p.s.i. and slowly reduce the O2 supply. The alarm should sound between 24 p.s.i. and 28 p.s.i.

3.6 If no alarm sounds, loosen the jam nut and turn the O2 adjuster (located under the air inlet) counterclockwise slowly until the alarm sounds.

3.7 If the alarm sounds when the gas supply is turned on, turn the O2 adjuster clockwise until the alarm stops, then turn counterclockwise just until the alarm sounds.

3.8 Reduce O2 pressure to 0 and relieve pressure within the hose.

3.9 Open O2 pressure to 50 p.s.i.; the alarm should stop sounding at or before 40 p.s.i.

3.10 Tighten the jam nut over the O2 calibration adjuster to secure calibration.

3.11 To calibrate the bypass alarm air calibration adjuster, repeat the process, replacing air for O2 in the instructions and remembering that the air adjuster is located under the O2 inlet.

4.0 Testing for Mixer Function

4.1 After all calibration procedures are completed, perform the Pressure Balancing Module test procedure.

4.2 The SECHRIST 3500 is now calibrated and ready for use.

During calibration of the Pressure Balancing Module, use a precision caliper to measure the thickness of the diaphragm assembly. Locate that measurement in the table below to find the corresponding depth micrometer setting for your mixer model.

DIAPHRAGM THICKNESS	MICROMETER READING
	3500 LOW FLOW	3500HL HI/LO FLOW
.810	.3975	.3850
.809	.3970	.3845
.808	.3965	.3840
.807	.3960	.3835
.806	.3955	.3830
.805	.3950	.3825
.804	.3945	.3820
.803	.3940	.3815
.802	.3935	.3810
.801	.3930	.3805
.800	.3925	.3800
.799	.3920	.3795
.798	.3915	.3790
.797	.3910	.3785
.796	.3905	.3780
.795	.3900	.3775
.794	.3895	.3770
.793	.3890	.3765
.792	.3885	.3760
.791	.3880	.3755
.790	.3875	.3750

Before servicing, be sure all exterior connections are disconnected.

Disassembly into 3 Major Modules

1. To remove the Alarm Module, use a 7/64″ allen wrench to remove the 2 screws securing it.

2. Slide the Alarm Module straight back to clear the bypass nipple and lift it off the Mixer.

3. Remove the 2 screws from the faceplate and remove the faceplate from the Mixer.

4. Using a 9/64″ allen wrench, remove the 4 screws from the Proportioning Module and separate it from the Pressure Balancing Module, making sure not to displace the O-rings.

Proportioning Module Disassembly

1. Using a 1/16″ or 5/64″ allen wrench, release the knob by removing the set screw(s); pull off the knob.

2. Use AT. 2 to insert into the front seat. Use a 1/2″ open end wrench to turn the spanner wrench and remove the front seat.

3. With the front seat removed, the double tapered needle will fall out.

4. Turn the module over to the rear seat.

5. Insert AT. 3 into the rear seat locking nut and loosen it using a 3/4″ open end wrench.

6. With the locking nut loosened, insert AT. 2 into the rear seat. Unscrew and remove the rear seat.

Pressure Balancing Module Disassembly

1. The Proportioning Module, Alarm Module, and faceplate must be removed first.

2. Using a 3/16″ allen wrench, remove the 4 screws from the air block.

3. The module will now come apart into 3 sections: air block, oxygen block, and diaphragm assembly.

4. Using tru-arc pliers, remove the tru-arc ring.

5. The cover disc will pop up, and the spring and regulator needle can be removed.

6. Using a 5/64″ allen wrench, loosen the set screw from the side of the block.

7. Using AT. 1, remove the eccentric adjuster.

8. The regulator seat can now be removed from either end.

Alarm Module Disassembly

1. Using tru-arc pliers, remove the tru-arc ring.

2. Remove the reed cap with the reed and reed retaining ring; do not disassemble the reed cap.

3. Using AT. 2, loosen the outside jam nut. Using AT. 1, remove the adjusters.

4. Using AT. 2, remove the adjustment cap cover.

5. Remove the spring.

6. Carefully remove the poppet. Carefully wedge the poppet out of the bore using a small allen wrench.

7. Using AT. 1, remove the check valve retainer.

8. Remove the spring from the check valve retainer bore.

9. Remove the ball from the check valve retainer bore by forcing high pressure air through one of the poppet bores. CAUTION: DO NOT ATTEMPT TO DIG BALL OUT OF HOLE: DAMAGE WILL OCCUR.

Before reassembling, inspect all O-rings. Replace any O-ring that is cut, flat, or worn, and apply a light coating of Krytox lubricant.

Reassembly of Proportioning Module

1. Using AT. 2, install the front seat into the front seat port (identified by the presence of two stop pins), making sure not to tear the O-ring. Do not install the knob at this time.

2. Turn the adjustment shaft counter-clockwise until resistance is felt.

3. Place the Proportioning Module front seat down on a level surface.

4. Drop the double tapered needle into the rear seat port and make sure the needle is standing up straight in the center of the valve bore. CAUTION: DAMAGE MAY OCCUR IF NEEDLE IS NOT STRAIGHT UP AND CENTERED.

5. Install the rear seat into the rear seat port, working it carefully so the needle stays centered. Using AT. 2 (hand tighten only), screw the rear seat down (about 6 turns) past the first resistance until contact is made with the needle. In this position, back off 1/2 turn.

6. Calibrate the Proportioning Module.

Reassembly of Pressure Balancing Module

1. Place the regulator seat in the regulator seat port, centering it in the block bore, with the small opening of the regulator seat towards the inside of the block.

2. Install the eccentric adjuster, making sure it is flush with the block. If not flush, rotate with AT. 1 until it drops into place.

3. Install the regulator needle, spring, cover disc, and tru-arc ring. Make sure the O-ring is in position in the machine groove.

4. Calibrate the regulator needle in the air block and oxygen block.

5. Center the diaphragm assembly into the center of the oxygen block, with the oxygen block flat.

6. Install the calibrated air block over the diaphragm assembly.

7. Install 4 screws to the module (hand tighten).

8. Using a soft mallet, position the 2 blocks so that they are flush.

9. Tighten the 4 screws in a cross pattern to evenly distribute pressure.

Reassembly of Alarm Module

1. Install the ball in the check valve retainer bore.

2. Drop the spring in the check valve retainer bore.

3. Using AT. 1, install the check valve retainer.

4. Insert poppets, small end first, into the poppet bores.

5. Install the spring into the center of the poppet.

6. Using AT. 2, replace the adjustment cap cover.

7. Using AT. 1, install the adjuster, turning until resistance is felt (about 3 turns). From this position, back off 1/2 turn.

8. Using AT. 2, tighten the jam nut over the adjuster (hand tighten only).

9. Calibrate the module at this time.

General Reassembly of Mixer

With all modules serviced and calibrated, reassembly can be completed in the reverse order of the disassembly procedure.

Routine maintenance is limited to periodic checking and changing of the inlet filters and general cleaning. Refer to the Test Procedure and Troubleshooting Guide Section to determine if replacement is needed.

Inlet Filters

1. Periodically replace the air water trap/inlet filter as needed.

2. Replace the internal sintered stainless steel filters as needed.

NOTE: It is recommended that the internal filters be removed one at a time to be sure that the inlet assemblies are not interchanged.

Cleaning

Exterior surfaces of the Mixer can be cleaned with a mild soap solution or wiped with a liquid disinfectant solution. Do not use cleaning agents that contain abrasives.

CAUTION: DO NOT IMMERSE THE MIXER. DO NOT GAS OR STEAM STERILIZE; DAMAGE MAY RESULT.

PART NAME	PART NUMBER	QUANTITY
PROPORTIONING MODULE:
O-ring	3548	1
O-ring	3513	5
O-ring	3521	2
O-ring	3534	4
O-ring	3520	1
Washer	3535	1
Adjustment Shaft	3533	1
PRESSURE BALANCING MODULE:
O-ring	3521	4
O-ring	3517	2
O-ring	3566	2
O-ring (wall mount)	3626	2
O-ring (inlet)	3520	2
Spring (Low Flow)	3515	2
Spring (Hi/Low Flow)	3612	2
Diaphragm Assembly	3510	1
Check Valves	3525	2
ALARM MODULE:
O-ring	3639	3
O-ring	3548	2
O-ring	3618	2
O-ring (reed)	3569	1
O-ring	3520	4
Alarm Reed	3560	1
Spring	3619	2
Spring	3637	1
Check Ball	3636	1
FILTRATION SYSTEM:
Water Trap Filter	3529E	1
Air and O2 Inlet Filter	3522K	2
FLOWMETER BLOCK:
O-ring	3578	1