VIBRATION ANALYSIS OF FIRE PUMP OF PEM AKAMIGAS CEPU: A CASE STUDY

Fire pump is a pump that is used to move water from the firewater reservoir to the location of the fire. If there is damage to this pump, the fire that occurs cannot be resolved quickly so that the impact of damage caused by fire becomes more widespread. Various problems can occur in the operation of the pump, one of which is damage to the bearings and shaft, noise occurs, decreased capacity, and even a decrease in pump efficiency. So to prevent the risk of greater damage and minimize losses in terms of cost and time, it is necessary to carry out maintenance. One of the efforts to detect damage to the pump is by vibration analysis, where from the vibration characteristics that occur, the type of damage can be determined. The purpose of this study was to determine the vibration characteristics that occur in the PEM Akamigas Cepu fire pump, by monitoring conditional vibrations using a vibration analyzer. The method is to attach the transducer to a predetermined location to determine the vibration spectrum that occurs in the axial, radial and tangential directions, then analyze the type of damage so that appropriate maintenance actions can be taken. As a result, this pump is indicated to be experiencing extreme looseness or bearing clearance problems at the pump drive end and pump non drive end as well as experiencing moderate pump imbalance, so it needs to be repaired immediately to avoid more serious damage.


INTRODUCTION
Predictive maintenance is maintenance by predicting machine damage based on an analysis of the operating conditions of an equipment, predicting damage, determining further maintenance, it is very important to find out early damage that occurs to equipment before it experiences serious damage, so it does not cause greater damage (Salami et al. 2021).Predictive maintenance is usually carried out using direct observation or sophisticated equipment, as was done to find problems with damage to the sucker rod circuit, a dynamometer is used to measure the path that occurs on the SRP, and efforts are immediately made to solve the problem on the SRP (Melysa and Musnal 2019).
Another way to observe the condition of an equipment is by vibration monitoring.With vibration analysis the damage that occurs to the pump in the form of clashes, misalignment, mechanical looseness, bent shafts, bearing damage, worn gears, and cavitation can be identified for proper further treatment.
The fire pump in the Polytechnic of Energy and Mineral Akamigas area is used to distribute air to the fire hydrant or fire extinguisher system in the lecture building.If this pump is damaged, then the fire that occurs cannot be overcome quickly so that the impact of damage due to fire will be more widespread.Since the pump is operating, the noise from this pump has increased, this noise can be caused by damage to pump components or pumps that have problems causing vibration and noise, therefore it is necessary to carry out maintenance because the slightest damage can cause greater damage, structural repairs when the pump is damaged larger ones will take longer and be more expensive.
Vibration analysis to predict damage to rotating equipment has been widely carried out (EDE et al. 2010), (Tenali, Babu, and Kumar 2017), (Carnegie et al. n.d.), (Noe and McKeirnan Jr. 1996), as well as vibration analysis to research specifically or researching vibration on certain components, such as the effect of misalignment variables (Akbar et al. 2021) and vibration on motor bearings (Mara, Catur, and Zulkarnaen 2018).Vibration analysis is carried out using various techniques such as MEMs accelerometer (Chaudhury, Sengupta, and Mukherjee 2014), spectral analysis (Salami, Gani, and Pervez 2001).
In this study, a vibration analysis will be carried out to predict the initial damage of the PEM Akamigas Cepu's fire pump, using the spectrum generated by the vibration analyzer.

A. Machine Damage Vibration
Characteristics The vibrations that occur will produce a spectrum.From the spectrum of running speed and lower frequency harmonics/multiple, it can be seen that the causes of vibrations in equipment such as: misalignment, imbalance and others.While the bearing frequency is FFT spectrum information to identify bearing damage that occurs at high motor speeds.
The vibration signal can be broken down into its component parts using the frequency domain.Each machine breakdown or malfunction creates a unique vibration signal, also known as a "signature", which can be used to identify machine failures such as: imbalance, bent shaft, eccentricity, misalignment, backlash, bearing malfunction (bearing defect), belt drive problem, failure gears, electrical disturbances, oil whip/spin, cavitation, shaft cracking, rotor friction, resonance, hydraulics, aerodynamic forces and others.

B. Imbalance/ Unbalance
Vibration due to rotor imbalance is probably the most common machine defect.Fortunately, easy to detect and easy to repair, for any type of imbalance the FFT spectrum will show a predominant vibration frequency of 1xRPM.
The vibration amplitude at 1xRPM will vary in proportion to the square of the rotational speed.These vibrations are always present and usually dominate the vibrational spectrum (Figure 1).

C. Mechanical Looseness
This problem is related to loose pillow block bolts, cracks in the frame structure or bearing bearings.Figures 3 and 4 show how high the harmonics are generated by the rocking motion of the pillow block with loose bolts.

E. Vibration Measurement Standards
The measurement standard aims to determine the permissible vibration level limit, from the measurement results it can be seen what actions we take, whether it needs repair or can it still be operated.

CONCLUSION
Based on the results of the study it can be concluded that: 1. from this study, and always monitor the increase in vibration that occurs.
The standard used in this study refers to the ISO 10816-3 standard -ISO Guideline for Machinery Vibration Severity.The use of ISO 10816-3 vibration standards is based on the type of machine (type and type of drive) and the foundation of the equipment, which are grouped into 4 groups, as shown in Figure7.These include:• Group 1: Large engines with engine power of 300 kW to 50 MW and with a rigid and flexible foundation.• Group 2: medium engines with engine power of 15 kW to 300 kW and with rigid or flexible foundations.• Group 3 : Radial, axial, mixed flow pump with power < 15 kW, with external driver • Group 4: Radial, axial, mixed flow pumps with power < 15 kW, with integrated driver.

Figure
Figure 8. Vibration Measurement Scheme
The fire pump belonging to PEM Akamigas Cepu experiences Mechanical Looseness or Bearing Clearance Problems in alarm conditions, both at the Drive End and the Free End, especially at the Drive End which is in the red area,