Regulator User Manual and Instructions

CREST Support and Service Center
Regulator Product Manual
Before diving with these diving equipment, please read and understand our product owner's manual completely.
Every time you use our products, please follow the specifications or recommendations in the product user manual.

Safe Dive!

This product user manual is applicable to the following models:
first stage head
second stage head
AC-10P, AC-10C, AC-20P, AC-20C

Your CREST regulator is warranted by CREST. This warranty applies to the original purchaser only and is non-transferable.
For more information, be sure to read the Repair and Service section of this manual.
Please keep your sales receipts, copies of these receipts must be submitted at the time of repair service.
Your regulator is in great need of regular care and maintenance.
Before starting to use a new CREST regulator, it is important to read this entire manual to familiarize yourself with the function of the regulator and to understand the proper procedures for pre-dive inspection and post-dive maintenance of the unit.

Warnings, Cautions, and Precautions

Pay special attention to terms or matters marked with warnings, cautions, and special fonts or symbols, such as:

⚠️Warning is used to inform a process situation which, if not avoided, may cause serious injury or death to the user.
⚠️ Be careful to inform any situation or technology that may cause damage to the product and may cause injury to the user.
⚠️Attention is used to emphasize, prompt and remind key points.

CREST Regulator Precautions Instructions and Warnings

Before diving with this regulator for the first time, please read and understand this manual carefully.

And in every use process, follow the specifications or suggestions in this user manual.

⚠️Before use:

  1. If you do not fully understand how to use this regulator, or if you have any questions, please ask CREST authorized dealers for assistance before using this product.
  2. You must have successfully obtained scuba diving approved diving technique training and certification before using this regulator.
  3. This product should not be used by persons who are not trained or who do not understand the potential dangers of scuba diving, as your ignorance of the risks of diving may lead to potential risks and dangers.
  4. This regulator is not intended for commercial diving use with surface-supplied equipment.
  5. Please note that before each dive, you must first check whether the equipment and functions are operating normally. If you find any problems or abnormalities, please stop using them immediately!
  6. Please note that before diving in cryogenic temperatures (below 50°F or 10°C), you must be trained and certified in an approved cryogenic diving technique.
  7. This equipment has only been tested and certified to a maximum depth of 50 meters (165 feet).

⚠️In use:

  1. This regulator must be used with a residual pressure gauge to measure and display the user's air supply pressure.
  2. When pressurizing the regulator, open the cylinder switch slowly .
  3. Do not stand the cylinder unsecured with the regulator on the cylinder valve, permanent damage to the regulator or cylinder valve may result if the cylinder falls over and hits the first stage of the regulator. Do not use the regulator as a handle when you need to lift or transport cylinders .
  4. As with all underwater life support equipment, improper use or misuse of this product can result in serious injury or death.

⚠️After use:

  1. Do not use any type of aerosol spray on the regulator as it may cause permanent damage to some plastic parts, including the second stage housing.
  2. This regulator must be serviced at least once a year by a specially trained technician authorized by CREST.
Statement of Compatibility of Regulator Equipment with Nitrox Diving

⚠️Parts of this instruction manual contain important information about equipment that uses gas mixtures of oxygen and nitrogen (Nitrox) higher than the oxygen content of air (>21%), but does not include air with an oxygen content of more than 40%.
⚠️Before you read and understand this instruction manual, please do not attempt to use this product in enriched oxygen air, otherwise the risk of injury or death will increase.
⚠️Those who have not been trained or do not understand the potential dangers and hazards of scuba diving should not use this regulator.
⚠️Users must have received or must obtain a Nitrox certification from a certified training provider prior to using regulator equipment containing nitrogen-oxygen breathing gas mixtures with an oxygen content greater than 22%.
⚠️ When the breathing mixture contains more than 22% oxygen, you must use a nitrox regulator according to EN 13949.
⚠️This regulator is not a medical device, it cannot be used to provide therapeutic oxygen in a medical emergency.
⚠️When using this regulator device, according to the EN250:2014 specification, the air used must meet the standard of EN12021 Table A.
⚠️be careful According to EN 250, the SCUBA shall be equipped with at least the following:

  1. Cylinder with switch and loadable frame
  2. Gas flow regulators such as first and second stages
  3. Pressure indicators, such as residual pressure gauges
  4. Carrying systems such as harnesses, harnesses, etc.
  5. Face mask, either mouthpiece or full face mask or diving helmet
Regulator Equipment Instructions for Use
first stage head

The function of the first-stage head is to convert the high-pressure air of the gas cylinder into an intermediate pressure of 135~145 psi, and after being processed by the second-stage head, it provides a stable breathing air flow during inhalation. Medium pressure air can also be used to inflate BCD or dry suits.
⚠️Warning Please prepare your first stage for use in a clean workplace.
⚠️Warning Do not connect a low-pressure hose to the high-pressure port (marked HP) or a high-pressure hose to the low-pressure port.

  1. Balanced and co-flow second stages are designed to run at 135 to 145 psi.
  2. Low pressure and high pressure port thread sizes are different.
  3. Please use a high-pressure tube to connect the high-pressure port. (Make sure to only place high pressure fittings or hoses in ports marked "HP" or "4500 psi / 300bar") and use low pressure tubing to connect to the low pressure port.
  4. After determining the hose type and installation direction, use a 4mm hex wrench to turn the plug on the first stage head counterclockwise, and keep the plug for future use.
  5. Turn the hose clockwise into the port to secure, then tighten with an appropriately sized wrench and torque to 30in-lb.
    Second stage: Hose external thread (3/8-24) internal thread (9/16-18)
    Inflation and exhaust valve (BC pipe): hose external thread (3 / 8-24)
    Residual pressure gauge: external thread (7/16-20)
  6. Once all the hoses are connected, test the complete regulator assembly by connecting it to the scuba diving tank.

Regulator connection to cylinder


Yoke: Maximum working pressure 3500 psi / 232 BAR
Din: Maximum working pressure 4500 psi / 300 BAR

Before connecting the regulator to the cylinder, please open the cylinder slowly for a second and then close the cylinder valve to let the high-pressure air blow off any moisture or dust on the cylinder valve.

YOKE: Check the sealing O-ring on the cylinder switch to make sure it is not aged or damaged. If O-ring is damaged, replace it.
DIN: Check the threads in the switch to make sure the threads are smooth and not chipped, otherwise you may damage the threads on the adjuster DIN head. Check the sealing O-ring on the DIN head to make sure it is not deteriorated or damaged.

Connect the regulator to the cylinder

Install the first stage:

Turn the handle counterclockwise to remove the dust cap from the YOKE head.
Connect the YOKE head to the cylinder, and cut the high-pressure inlet plane of the first stage head to the O-Ring of the cylinder valve, and turn the knob clockwise until it is secure.

Remove the dust cap from the DIN head and inspect the threads and O-ring. If the O-ring is damaged, replace it.
Screw the DIN connector into the cylinder valve clockwise, the knob until secure.

After installing the first stage, follow these steps:

  1. Slowly turn on the gas cylinder switch, please pay attention to or stay away from the residual pressure gauge.
  2. Briefly press the second stage vent soft cap and listen carefully to make sure no gas is leaking from the regulator or cylinder.
  3. If leaks are found, check the sealing O-rings and replace if damaged or improperly sealed.
  4. If the leak persists after replacement, do not continue to use and take the regulator and cylinder to an authorized supplier or dealer for inspection and repair.


Remove the regulator from the cylinder

Turn off the cylinder switch and press the soft cap of the second stage to purge all air, making sure all pressure is removed.

Turn the knob on the YOKE head counterclockwise, loosen it, and remove the first stage head from the gas cylinder.
⚠️Be careful not to use air to blow to the air inlet of the first stage to prevent seawater salt or impurities from entering.

Turn the DIN head counterclockwise out of the gas cylinder and remove it from the gas cylinder valve, and immediately install and lock the dust cap of the header.
⚠️Be careful to install the dust cover immediately to prevent water and impurities from entering the first stage.


Remove the hose from the first stage

⚠️Warning Remove all pressure from the first stage before attempting to remove the hose and remove it from the cylinder.

  1. Loosen and remove the hose by turning it counterclockwise with the appropriate size wrench:
    Low-pressure pipe: use a 3/8 open-end wrench High-pressure pipe: use a 7/16 open-end wrench.
  2. Lightly lubricate the threads and O-rings on the end with Christo-Lube MCG129 Lubricant.
  3. Thread the port plug clockwise into the port and tighten to 30 in-lbs, using a 4mm hex wrench.
  4. Store dry regulators in a clean bag or moisture-proof box away from sunlight, heat, and humidity.

second stage head

The second stage of the regulator set receives approximately 140 psi medium pressure, breathable air from the first stage, converts it to ambient pressure for you during your inhalation, and then stops the pressure delivery during your exhalation, And the exhaled gas is discharged through a specific path.

⚠️ Note
All second stages have a certain sensitivity and when the second stage is not in your mouth it can cause excess air to be released into the water, this phenomenon is known as the Venturi effect and usually occurs when entering or on top of the water.
If this happens, turn the second stage so that the mouthpiece faces down and the exhaust valve faces up.

⚠️ Note
The balanced second stage head can use the Venturi adjustment knob (spoiler knob) to turn to "min" or "pre dive" to solve or reduce the Venturi effect.

⚠️ Note
If you carry a spare second stage (spare air source) with you, it is recommended to face the mouthpiece down when not in use, or turn the Venturi adjustment knob (spoiler knob) to the lowest setting or use a mouthpiece plug or cover to protect against collisions Air leaks from time to time.

⚠️ Note
During normal use underwater, a small amount of water may collect on the bottom inside the regulator, which is normal for most second stages.
You can exhale vigorously to expel the water, or place your tongue against the mouthpiece and press the release button briefly to force the air out.

Venturi adjustment knob (spoiler adjustment knob)

The Venturi adjustment knob can adjust the airflow direction of the air supply during inhalation, manually adjust the airflow direction according to the demand and usage conditions, or reduce the Venturi effect.


  1. At this time, the airflow is towards the mouth, and the user will receive more air volume.
  2. We recommend turning this knob to this position when the second stage is in use and in your mouth.


  1. At this time, the airflow is directed to the other side of the mouth, and the impedance is slightly increased, which can prevent or reduce the Venturi effect.
  2. We strongly recommend turning this knob to this position when the second stage is not in the mouth.

Impedance adjustment knob

The impedance adjustment knob can manually fine-tune the breathing resistance. When the user turns clockwise, the breathing impedance will increase, and the user must use greater force to breathe; on the contrary, turning the knob out, the breathing impedance will decrease.


Clean or replace the top cover and soft cover

If you want to clean or replace a flip or soft cover of a different color (or style), follow the steps below.
⚠️Warning When replacing, the regulator must never be connected to the gas cylinder.

  1. Rotate top cover from housing (no tools required)
  2. Remove soft cover and wash
  3. Choose your top or soft cover
  4. and install the diaphragm spacer inside the assembly to the top of the diaphragm
  5. Turn the upper cover onto the housing and tighten it by hand

Assisted Emergency Respiratory System

For safety reasons, a suitable alternative breathing air (gas)/assisted life support system is recommended when using self-contained underwater breathing apparatus (scuba diving).
This advice will vary depending on where you have been trained and the training institution, and you must follow your training style. However, the use of a secondary emergency breathing system (also known as an alternate air source or alternate second stage) is very common during both recreational and commercial diving.
The backup air source is a backup second stage designed to be used with the main second stage and both are connected to the first stage.
The backup second stage is to provide backup in the event of failure of the primary second stage and can act as an Alternate Air Source (AAS). In the event of a buddy regulator failure or air leak, the lead diver does not need to move the original cylinder valve. By its very nature (except during training) this type of equipment should only be used in emergency situations and therefore may experience very high breathing demands as it may need to support two divers breathing simultaneously.
As stated in the minimum safety requirements for this type of product, use of a spare second stage in water temperatures below 10°C (50°F) and depths of 30m (98ft) presents significant risks and is therefore not recommended .
Although these minimum requirements only require testing and are limited to 30 meters (98 feet) and 10°C (50°F), CREST recognizes that emergencies may exceed these limits.
The CREST main regulator and auxiliary emergency breathing system are designed according to the requirements of EN250:2014 Annex B, with a depth of 30 meters and a water temperature of 4°C.
To ensure that CREST products perform as well as possible in all situations, CREST designs products that exceed at least the minimum security requirements. This does not mean that the backup second stage will match the performance of the primary second stage in water temperatures below 4°C (39.2°F) and depths greater than 50m.

⚠️Warning If the scuba diving equipment is used by several divers at the same time, it must not be used at depths greater than 30 meters and in water temperatures below 4°C.
As a user, you can be confident that in an emergency or low-gas situation, your regulator will provide what another diver needs to assist with the emergency breathing system (back-up air source), and will provide support for all situations you may face. You safely provide enough gas.

⚠️Warning If assisted emergency breathing systems (alternate air sources) are used, you must ensure that the equipment selected is designed and tested for use with assisted emergency breathing systems, is suitable for the water temperature and depth, and can be used as an escape device by multiple divers at the same time.
Your equipment is subject to maintenance according to the manufacturer's recommendations, usually annual inspection and service.

User Care and Maintenance

⚠️ Note Please provide proper preventive maintenance to ensure the best performance and longest life of your CREST regulator.
The following maintenance procedures should be performed periodically after each use to ensure the regulator is clean, inspected and ready for next use.

  1. Whenever the regulator is removed from the cylinder, a dust cap must be installed on the regulator fitting, this is to prevent moisture from entering the first stage.
  2. When not in use, the dust cap should be installed on the first stage to prevent moisture.
  3. The dust cap must be completely wiped or blown dry before attaching it to the joint.
  4. Rinse the regulator thoroughly with clean water as soon as possible after a dive while it is still attached to the tank.
  5. Place your regulator (preferably dry) in a padded suitcase or equipment bag during transport and separate it from sharp objects to avoid damaging or scratching parts.
  6. The second stage should be protected from being crushed by heavy objects.

pre-dive check

CREST regulators must pass a visual inspection and functional test before each use, if the regulator shows signs of damage or provides substandard performance, do not dive with this regulator and return it to CREST or an authorized CREST dealer repair.

Pre-dive Checklist
  1. Carefully inspect all hoses and their fittings to make sure they are securely connected to the first stage.
  2. Check the length of each hose to make sure the hose is not blistered, cut or damaged. If you have a hose cover, slide the cover back to expose the hose connector and check the hose as above.
  3. Visually inspect the first stage and second stage regulators for any signs of external damage.
  4. Sealed Intact First Stage: Carefully inspect the outer sealing diaphragm for any signs of damage or deterioration that could lead to air leaks. Check to make sure the retainer holding the outer diaphragm is securely fastened.
    ⚠️WARNING : If the external diaphragm shows any signs of damage or neglect, do not attempt to dive with this regulator until it has received factory prescribed repair service from an authorized dealer. In cold water conditions, the first stage may freeze and the function of the regulator may be affected.
  5. Connect the first stage to a filled cylinder, (for installation instructions, see section Regulator to cylinder) and slowly turn on the cylinder switch to pressurize the regulator. Continue to turn the switch counterclockwise until it reaches the end, this is to ensure that the switch is fully on.
  6. After turning the cylinder knob (counterclockwise) to the end, turn it back (clockwise) one turn, this is to make the regulator less prone to leaks when providing maximum breathing comfort. Do not apply excessive pressure.
  7. When the Venturi effect function is set to PRE-DIVE, the regulator can be purged immediately to expel any dust or debris that may have entered the second stage. Release the soft cap clear button and listen to make sure there is no second stage leaking when the soft cap is released.
  8. Inhale air through the regulator several times and slowly. The regulator must provide enough air for you to breathe easily without significant resistance.
  9. Check to make sure the residual pressure gauge is accurately measuring the air pressure in the cylinder.
  10. Check to make sure the Venturi knob is set to PRE-DIVE and turn the impedance adjustment knob slightly (clockwise) all the way to the end. Do not rotate too vigorously. These settings will help reduce any loss of air supply when entering or swimming for extended periods of time. This step can also be adjusted underwater.

Things to check when diving

When you're ready to dive in, put the second stage in your mouth and set the Venturi knob to your desired position.
Turn the Inspiratory Resistance Adjustment Knob outward (counterclockwise) until the regulator allows for comfortable breathing without leaking or discomfort.
As you descend, you may need to turn the inspiratory resistance control knob up again to breathe easier. This is especially true at deep dives where the air density increases.

Repair and Maintenance Services

If there has been little use since the last service and maintenance service, there is no guarantee that the regulator will be in good condition.
Remember that long-term or improper storage can still cause internal corrosion and O-ring deterioration.

If any part of the regulator requires repair or service, return it to an authorized CREST supplier or dealer for professional repair.
If corrosion or contaminant residue is found on the filter surface, it is strongly recommended not to dive with this regulator and to return it to a CREST authorized supplier or dealer for professional repair.
All maintenance and warranty services must be performed by CREST-authorized suppliers or distributors, and by technicians authorized and trained by CREST.
Your regulator assembly should be inspected and serviced annually by a CREST authorized supplier or distributor.
If your regulator is being used for rental or training purposes, it will require a complete overhaul and factory prescribed repair and maintenance every three to six months.
Chlorinated swimming pool water is a particularly hazardous environment for scuba diving equipment. High levels of chlorine and pH balance can cause some parts to deteriorate quickly.
If you dive in rough conditions or dive more frequently than the average diver, it is recommended that more frequent service and maintenance services be required.
⚠️Warning Do not attempt to disassemble or repair the regulator yourself, otherwise it may cause the regulator to malfunction and void the warranty service provided by CREST.
⚠️Note to individual owners for recreational diving activities:
Equipment that is used less than 100 times per year should be serviced at least once a year.
It should be repaired and maintained after 100 dives each time before it can continue to be used.
⚠️Attention equipment owners used for diving training or consumer rental activities:
Equipment should be inspected before each use.
Regardless of usage, equipment should be serviced at least every six months.
The equipment should undergo further maintenance after 100 dives.
Equipment stored for more than three months should be inspected and repaired before use.
If it shows any signs of air leaks or failure, the unit should be inspected and repaired.
If the first stage filter inlet shows any residue or signs of corrosion, the unit should be inspected and repaired.
If the equipment shows signs of improper performance or breathing difficulties, the equipment should be inspected and repaired.
If the seals or hoses show any signs of deterioration, the unit should be inspected and repaired.

Warranty and Limitation of Liability

This product is provided with limited liability warranty by CREST. For the warranty method and details, please refer to the attached product warranty.

Limited Warranty Coverage:

  1. Only authorized agents or distributors of CREST are applicable to the scope of CREST product warranty and after-sales service, and enjoy a two-year product warranty from the date of shipment. During the warranty period, damages and failures caused by product defects will be repaired by CREST free of charge, or replaced with new products or products of similar value.
  2. CREST warrants only to the original purchaser that the product will be repaired or replaced free of charge if the product proves to be defective for any reason, under normal use in recreational diving, with proper care and maintenance, from the date of purchase, against material defects. If the device has been tampered with by non-CREST authorized service personnel.
  3. This warranty is void if the device is used for rental, military or commercial purposes.
  4. The scope of product warranty does not include: product packaging, product appearance, pipelines and consumables, and non-body accessories.
  5. The product warranty does not cover: loss, theft, damage caused by accidental damage, abuse, tampering, lack of maintenance, exposure to excessive heat, excessive sunlight, or use of inappropriate chemicals.
  6. The warranty will also be invalidated if the repair service is performed by a non-authorized agent or dealer of CREST.
  7. The company is not responsible for restoring or replacing lost or stolen products.
  8. This free warranty service does not include the costs of normal repairs, inspections and preventive maintenance.
  9. Products that have been repaired and maintained by the product warranty are still based on the original shipment date as the basis for calculating the warranty period. After the product warranty expires, it still belongs to the service scope of CREST. For maintenance and repair, please contact local distributors.

In order to ensure your product warranty rights, please pay attention to:

  1. For products that our company provides service guarantee, please register online for warranty service.
  2. Or you must have the original retail purchaser's purchase receipt to obtain warranty service, and the proof must include: authorized dealer or retailer's store name, original retail purchaser's name, purchase date, product model, part name, purchase price and other relevant information . If the above information is incomplete, or the text is unclear or vague, CREST has the right to refuse maintenance.

This warranty gives you specific legal rights, which may also have limitations that vary from country to country.
If you have any concerns about your limited warranty on your product, please contact

Copyright ©2023 Crest Inc. All rights reserved.

This user manual is copyright protected (©) 2021 CREST All rights reserved. This may not be reproduced, duplicated, translated or used in any electronic medium or machine-readable form, in whole or in part, without the prior written consent of CREST.

Regulator User Manual-2023.01.01