HP + LP air Flashcards
describe the 1 st stage filter fitted to a HP air dryer
- bulk liquid containment is revoked from the inlet air stream by a high efficiency vortex operation water separator which removes 90% condensate and aerosol contamination at 21 degrees celsius and 80% particulate removal
list and describe 4 functions in oil hudrovanve LP compressor
- lubrication - oil under pressure is fed to the moving parts
- cooling - oil injected into rotating assembly is in direct contact with air, oil absorbs heat from air which is then dissipated through the oil cooler
- sealing - oil helps to seal any gaps around the vanes, this maintains partial vacuum and high pressure within the cycle
- control - fluctuations in oil pressure us used to control the unloading device, this varies its output as demand requires
what is the correct routine to isolate a LP compressor
- stop the compressor and isolate from electrical supplies
- close the air outlet valve to isolate compressor from the air system
- open the relevant drain to vent pressure from the air cooler and pipe work
- check that the air end pressure indicator reads 0
- carry out tag out routine
describe how to carry out a HPAC performance trial
- a 6 monthly performance trail should be carried out and recorded to monitor the performance of each compressor
- test constitutes of a time trial based on compressor output
- hamworthy compressor delivers 115m^3/hr at inlet temp of 10 degrees
- the system must be configured to allow the compressor to fill one 258 litre cylinder from empty to 276 bar
- time required should be 32 mins, any deviation from this indicates problem and requires investigation
list and describe 3 operating modes of a HP air drier
heat regenerative mode
- preferred operating modes used during normal operation to supply high quality air to the ring main.
fully automatic with the outlet solenoid valve, hydrometer sensor, auto drains, heater circuit and keypad display all operational in this mode
total cycle time 2 hours 40 mins
heatless mode
- heater circuit is disabled in this mode
total cycle time is 40 mins
bypass mode
- use during maintained/emergency conditions. this mode disables the dryer control circuits but still maintained operation of inlet filter solenoid drain valves. the valves controlling the flow path through the bypass leg are manually operated and must be correctly portioned during bypass conditions
discribe how oil is removed from discharge of a LP compressor
- oil baffle plate - a metal cylinder fitted to outside of the stator,heavier oil strikes the baffle plate and drops to the bottom of the casing, this removes 99% of the oil
- coalesced filter - air passes through the filter removing remaining oil down to 5 ppm which then returns to the compressor casing through the oil return valve
what precautions must be observed when removing the oil filter plug on a hydro vane compressor
- when the compressor is running oil level should be visible in the sigh glass located in the intake air end
- if not visible stop the compressor and top up. Do not attempt to fill the compressor until the pressure gauge reads 0. Do not remove the plug until air pressure has drained from the unit
- if any air or oil escapes from the filter plug whistle undoing, stop and allow pressure to dissipate
- the compressor oil and filter should be changed every 2000 running hours
describe the factors that affect the efficiency of a HP compressor
- air filters - blocked or dirty filter prevents air entering the compressor which reduces output
- cooling arrangements- lack of cooling causes the cylinder walls to become hot. Air expands when comes into contact preventing full charge
- operation of cylinder valves- if valves not seated correctly air will leak past, compression will be lost
- worn piston rings/cylinder liners- wear or damage to these result in a loss of compression, reducing the compressor output
list the daily checks on a LP dryer
- check all gaskets, control valves, pipes and fittings for air leaks
-ensure changeover of the desiccant columns occurs approx every 2 mins - manually operate the pre-filter and after filter drains, check drains are clear
- ensure that the on-line colum pressure gauge reads between 7-8 bar
- ensure that the off-line colum pressure gauge reads 0 bar
- ensure moisture indicator crystals are blue
- check dew point reading on hygrometer, should be less than 40 degrees min
- check auto drains operating correctly
list and describe the safety devices on LP compressor
- A safety valve is fitted in the air output just before the discharge valve and is designed to safeguard themachines at 8.5 -10 bar
- the starter is fitted with an interlock which protects the compressor should the oil temp rise above 104 degrees and there is also a motor thermistor
- a thermal bolt is fitted in the discharge line which opens when the air temp rises above 125 degrees
list the routine to change the air filter on a LP compressor
- stop the compressor and isolate the electrical supplies
- unscrew the hand wheel and remove filter and seal cover from free end of compressor
- remove air filter element
- vacuum clean or blow dust from filter using LP air, clean and dry renew filter if due or if filter cannot be cleaned effectively
- wipe clean filter supports and inside of filter cover
- replace filter
- replace filter cover and seal, secure, assembled with hand wheel
describe the pressure vessel register
- details of all test requirements, periodicity and methods are details in BR200(89) compressed gas system design and engineering practices
- it is the responsibility of the user, ultimately the MEO/WEO to ensure that all the equipment listed in PVR are maintained in test date and that the register is up to date
- at no time must any equipment listed exceed their specified test date without appropriate dispensation from design authority
- all relevant test certificates are to be inserted in the PVR
describe separators fitted to a HP compressor
- fitted to HP compressors after the compression stage
- they are designed to cause moisture droplets carried in the air to fall out if suspension
- just bottles with the inlet pipe extended into the bottle
- as the air changes direction water drops to the bottom
what is the purpose of a minimum pressure outlet valve
- this valve ensures sufficient pressure is maintained within the compressor to generate oil circulation before allowing air to leave
- it also acts as a non return valve when the machine is stopped to prevent air draining back out of the ring main through the compressor
what are the general precautions when working on air systems
- stop the compressor and isolate from electrical supplies
- close the air outlet valve to isolate compressor from the air system
- open the relevant drain valve to vent pressure from the air cooler and pipe work
- check that the air end pressure indicator reads 0
- carry out tag out routine
